Stainless Steel in Architecture

Miettinen, Esko

Stainless Steel in Architecture

1 Stainless steel as a material
1.1 Stainless steel
Stainless steel is the common name for all steel grades containing at least 10.5% chromium. Chromium improves the corrosion resistance of stainless steels. In addition to iron and chromium, stainless steels contain other alloying metals, of which the most important are nickel and molybdenum. The combination of chromium and oxygen leads to the formation of a chromium-rich passive layer on the surface of the steel. This layer protects the steel, and re-forms over time if damaged.

On the basis of their microstructure, stainless steels are divided into austenitic, ferritic and martensitic basic types. More than 100 different stainless steel grades have been developed for various applications.

The contents of the alloying metals influence the corrosion resistance, durability, strength and formability of the steel. Ferritic steels, such as iron-chromium alloys are mainly used for indoor applications. Some grades are also used for roofing. Austenitic grades represent about 70% of the world market for stainless steels. These are iron-chromium-nickel alloys – some with additional alloying elements like molybdenum, which increases corrosion resistance even further. The most popular grades for building applications, like the classic “18/10” grade 1.4301 (about 18% chromium and up to 10% nickel) or the particularly corrosion resistant grade 1.4401 (with additional molybdenum content), belong to this family. For extremely demanding conditions, austenitic-ferritic steels, the so-called duplex steels, are the best choice. Their microstructure guarantees excellent strength and corrosion resistance..
Stainless steel is a preferred material for applications where the structure must have a long service life and be easy to maintain, or where a metal surface is desirable for aesthetic reasons. In addition to corrosion resistance, the use of stainless steel in construction is based on its mechanical durability, the fact that it is easy to clean, and on factors related to image and appearance.

The increase in the use of stainless steel is closely related to the rise in the standard of living. As standard of living and technical development are interdependent, the popularity of stainless steel can be assessed on the basis of technical development. A rising standard of living increases the quality awareness of individual consumers, which then increases the use of high-quality consumer durables, among them stainless steel products. Investment decisions are increasingly based on estimated total life-cycle cost.

Development
The first stainless steel grades were developed between 1910 and 1920. Krupp, the German, family steel company, patented the first austenitic (so-called 18/8) steel, containing both chromium and nickel. At about the same time, Harry Brearley in Sheffield, England, developed stainless steel grades used in the manufacture of cutlery. Thus, the first austenitic and martensitic stainless steels were developed just before the First World War. Industrial manufacture of stainless steel started in the 1920s.

Most of the standard stainless steel alloys in use today were developed between 1913 and 1935, in Britain, Germany, the United States and France. With the introduction of standard alloys, it was possible to concentrate on more economical production methods and on promoting the use of stainless steel.

The use of stainless steels in the chemical, process and food industries started towards the end of the 1940s and in the 1950s. Stainless steel products have been used in the home since the 1950s. However, it was not until the 1960s and 1970s that the use of stainless steel increased significantly, when it was adopted in vehicles, energy generation and the construction industry. The extremely strong and corrosion-resistant molybdenum-alloyed stainless steel grades became popular in the 1970s.

Applications
The most important applications of stainless steel include:
- the process and chemical industry
- the wood processing industry
- the food industry
- household utensils
- energy generation plants
- environmental technology
- transport and vehicles
- architecture and construction
- furniture
- medical equipment and instruments

Process and chemical industry
Equipment and tanks made of stainless steel find numerous applications in the handling and storing of various oils, gases and acids. Stainless steel offers better pressure resistance and corrosion resistance properties than other materials, in flow pipes, pumps, valves and tanks used in processes involving higher pressures or aggressive media. The paper and pulp industry is one example of an important sector of the process industry that makes extensive use of stainless steel equipment. The use of stainless steel within industry is also increasing in other applications, besides actual process-related equipment.

Food industry
In the food industry, stainless steel is used in the manufacture of equipment intended for the preparation and storage of foodstuffs. Stainless steel is one of the few materials to have been widely approved for use in the food industry. Neither foodstuffs nor the chemicals used in the preparation of foodstuffs will corrode the surface of the material, and stainless steel does not affect the quality of foodstuffs. Stainless steel surfaces are also hygienic and easy to keep clean.

Household utensils and furniture
Stainless steel has found many household applications, not only in utensils such as pots and pans and in cutlery, but also in decoratively designed products. Designers favour stainless steel both for its material properties and its aesthetic qualities.

Sink units are one example of a widely used stainless steel product. In the 1980s and 1990s, the use of stainless steel in furniture and fixtures increased significantly – particularly in wet areas but also in public lounges, office and the urban environment.

Energy and environment
Stainless steel is used abundantly by the nuclear power industry, both in the energy-generation process and in radiation protection – for example, in the final-disposal capsules of spent fuel bars. The long-term durability of stainless steel is a great advantage in energy generation plants.

One of the most recent and rapidly growing application areas for stainless steel is environmental technology. In collection, sorting and treatment processes, the long-term durability and recyclability of stainless steel provide significant benefits.

Transport and communications
The use of stainless steel is constantly increasing in the automobile industry. Its use is mainly in equipment subject to the influence of exhaust gases and, to some extent, now, in chassis structures. Stainless steel has an even longer tradition, and a wider range of applications, in the manufacture of other transport vehicles. The development of the aviation industry, in fact, contributed significantly to the development of stainless steel grades. In shipbuilding, stainless steel’s corrosion resistance makes the material highly economical for many applications.

Construction
In the field of construction and architecture, stainless steel is most commonly used on façades and roofs, in fasteners, fastening systems and concrete reinforcement bars, in glass structures, balustrades, stairs and balconies, as well as on interior surfaces and in HEVAC supplies. In load-bearing structures, stainless steel is continually gaining popularity.

Stainless steel is a very common material in offshore structures, being one of the few materials to maintain its properties in the demanding and humid chloride atmosphere found in this context.

Medicine
The medical industry employs various special stainless steel alloys that can be used in the manufacture of, for example, artificial joints. Various instruments are also made of standard stainless steel grades. Stainless steel is hygienic and easy to keep clean, and is a durable material, suitable for medical procedures in which absolute cleanliness is critical.

World trade
The annual global production of stainless steel was about 17 million tons at the end of the 1990s. Volume has grown steadily and vigorously ever since production first started, and is estimated to be growing by about 5% a year. In the past 30 years, the use of stainless steel has tripled, showing the most impressive growth rate among metallic engineering materials in the building industry.

At the turn of the millennium, the total combined production of stainless steels from European steel mills amounted to a little under 7 million tons a year. Stainless steel producing countries in Europe include Belgium, Finland, France, Italy, Spain, Sweden and the United Kingdom. In the United States, annual production of stainless steel is currently over 2 million tons, and in Japan, some 4 million tons. European mills export significant amounts of stainless steel to Asia and the United States. In fact, Western Europe and Japan are the leading exporters of stainless steel.

1.2 Materials
Steel grades and their properties
Austenitic stainless steels are more commonly used than other steel grades, owing to the broad scope of their application. Austenitic stainless steels contain 17-18% chromium and 8-11% nickel. This high nickel content makes them easy to form, without compromising strength. Their corrosion resistance is also very good. The strength of austenitic steels can be further improved by alloying them with nitrogen, or by cold-forming. Austenitic steels are easy to weld and are also tough at low temperatures. Another sub-group of austenitic steels contains molybdenum. Their excellent corrosion resistance in very severe conditions is based on a 2-6% molybdenum content.

Ferritic stainless steels contain chromium and, possibly, other alloying elements, but no nickel. They range from low-cost grades, near the lower end of the stainless steels spectrum, to stabilised grades used for household appliances. Typically, they are also used for interior cladding or with an additional matt tin layer for roofing.

Austenitic-ferritic (Duplex) stainless steels contain 22-23% chromium and 4-5% nickel, and often molybdenum (an important additional alloying element). These steels have excellent corrosion resistance and strength properties. However, they are only used in special applications and for extremely aggressive conditions.

Martensitic steels have the highest carbon content of all stainless steels, and are magnetic. The main applications of martensitic steels are in various small utilities, such as instruments, cutting tools, scissors, springs, etc. They are sometimes used for fasteners.

Stainless steel grades can be manufactured with alloying metal contents of up to 50%, which gives almost unlimited possibilities for regulating the steels’ properties. So, for instance, extremely corrosion resistant grades are even available for suspended ceilings of indoor swimming pools – one of the most demanding and complex corrosive conditions to be found in building applications. If the content of alloying metals added to iron exceeds 50%, the steels are called “super alloys.”

The most common composition of austenitic stainless steel, and also that which has been used longest, is 18% chromium and 8.5-10% nickel, referred to as “18/8” or “18/10” steel. These steels account for about two thirds of the total market. The most common stainless steel grade, EN 1.4301, is of this composition. Steel designations specified in European Standard EN 10088 are commonly used in Europe, whereas the AISI in the United States, for instance, has its own designation system. The longer Euronorm-based designations indicate the steel’s composition. For example, X5CrNi18-10 designates the steel grade and its most important alloying metal contents, while the shorter numerical designation for the same steel is 1.4301.

Manufacturing process
Stainless steel is manufactured largely from recycled steel scrap. The scrap and required alloying metals are melted in an electrical furnace and the molten steel is then transferred into an AOD (Argon Oxygen Decarburisation) converter for further refining. In the converter, the molten steel is decarbonised to a sufficiently low level, and all impurities that would impair the properties of the steel are removed. Once composition and temperature reach the desired level, the steel is cast. The steel’s composition is finally regulated, at ladle stage, by adding any required alloying elements and by verifying correct temperature and uniform quality.

The molten steel is then cast, cooled down and, finally, cut into slabs of suitable size in a continuous casting machine.

In hot rolling, the steel slabs are preheated to a temperature of about 1,250°C, to be hot rolled into a wide coil, 2-13 mm thick. After the hot rolled coil has been cooled down, it is heat-treated and pickled. The steel grade and manufacturing lot is marked on the steel, and the hot rolled steel is then ready for use or for further processing. In the building industry, hot rolled stainless steel is used for fasteners, such as brick support systems.

Most steel coils are cold rolled. Cold rolled steel is also heat-treated and pickled, and surface quality is improved, by dressing, to reach the standard required for high-quality consumer goods or architectural finishes. The finished coil is cut into plates or strips for delivery.

In addition to sheets and plates, stainless steel is delivered as rods and other long products such as reinforcement bars and rod wire, also produced by rolling. From these, stainless steel wires, of less than 5 mm diameter, are produced by drawing. These are typically found in architectural cables or woven metal fabric.

Surface finishes
In the steel mill, the steel is finished to a certain surface grade. These pre-production finishes are sufficient for most applications. The best way of assessing a surface finish is to ask the mill for a sample. Factory finishes can also be further treated, for various uses. The same criteria, of “no visible faults” and “rated corrosion resistance,” are applied to all steel finishes. This means that oxides created by the heat, as well as metal residues, have to be removed from the surface. This is usually done by treating the steel in an acid solution or by pickling. The designation for a hot rolled and pickled stainless steel surface finish is 1D, as specified in Standard EN 10088. The corresponding designation for a cold rolled and pickled steel surface finish is 2D. This smooth, matt surface finish is often used in industrial applications and, increasingly, in architecture, for example. Cold rolled steels can be further treated to increase surface polish and smoothness. For example, surface finish 2B is not only pickled but also lightly rolled in the skin pass mill. The most common of all surface finishes is 2B. Bright annealing can be used to produce an extremely glossy surface.

Surface treatment methods
After the steel sheet has been delivered from the mill, its surface can be treated before the sheet is sent for further processing, or post-production finishing can be carried out at the manufacturing stage of the actual product. If surface treatment is carried out before manufacturing stage, there is a risk of the surface being scratched or damaged in some way during the manufacturing process, or of the joints and corners requiring yet another treatment after manufacture. On the other hand, post-production finishing carried out before manufacturing stage usually gives a more uniform surface quality than does treatment carried out afterwards. This is particularly advantageous if there are extensive visible surfaces on the finished product.

Post-manufacture surface finishes are applied both to products made of untreated steel and to the repair of pre-finished surfaces after manufacture. However, the pre-finished surface may differ from the surface treated after manufacture, so it is advisable to apply post-manufacture surface finishing to all surfaces to be joined together.

Pickling is a surface finishing method also applied after delivery from the mill. Pickling may be used to remove heat tint from welding, for example, or contamination from carbon steel particles, which would affect a stainless steel’s corrosion resistance. The entire product can be pickled, or just local points, such as a joint.

An additional rolling operation can be carried out to produce patterns on one or both sides of the steel sheet, using patterned rolls. A patterned surface hides scratches and minor surface defects, which makes this treatment suitable for contact surfaces. Pressing is also used. Certain symmetrical patterns can also be applied, to stiffen the structure and thus allow the material thickness of the steel to be reduced.

Brushed and polished surfaces are produced, in one or several stages, using grinding bands, rolls or brushes. Several options are available, and the appearance, corrosion resistance and soil repellence of the surface may vary considerably, depending on the tools and methods used.

Sand and glass-bead blasting can be used to produce a matt finish on stainless steel. Surface texture is regulated by changing the roughness and quality of the blasting agent. For example, sand produces a dark and rough surface, while glass beads produce a smooth, light-coloured surface. Glass is preferable since it does not contain iron, which could be deposited on the stainless steel and affect its corrosion resistance.

Electrolytic polishing, or electropolishing, is used to produce technically smooth surfaces. The process is based on an electrochemical reaction, whereby a suitable electrolyte causes a thin layer to escape from the surface of the steel, which acts as an anode. Maximum use is made of the “natural” corrosion resistance of the respective grade. However, electropolishing is not used for decorative purposes and does not produce mirror-like finishes. For such finishes, bright annealed and mechanically polished material is available.

Stainless steel can also be coloured by means of an electrolytic process. This does not involve colour pigments, but is based on the optical effect of light interference. By building up different thicknesses of passive layer, a wide range of colours can be obtained. The layer is totally resistant to UV radiation. To achieve a good result, the surface must be smooth. There is, however, no possibility of repair if the colouring is locally destroyed through mechanical damage or welding.

Painted steel sheets are mainly used on roofs and as cladding elements.

Etching, bead blasting and laser technology can be used to produce patterns on stainless steel surfaces. This extremely accurate method offers unlimited patterning possibilities.

Steel products
Most stainless steel is used in cold rolled form. The roughness and unevenness of the surface of hot rolled stainless steel restricts its applications to non-decorative applications, such as fasteners.

Stainless steel is delivered from the mill as hot or cold rolled coils or plates. The material thickness may vary from 0.3 mm up to 13 mm, depending on the rolling method. The plates and coils are delivered either to the end-user or to further processing plants, for finishing or for use in the manufacture of finished and semi-finished products. These are then delivered to wholesalers or end-users. Stainless steel products include various hollow sections and profiles, rods and rolled wires, screws, bolts, concrete reinforcement bars and steel plates with different surface finishes. The diameter of steel rods and bars ranges from a few millimetres up to some 200 mm. Stainless steel reinforcement bars are available in the same stock sizes as carbon steel reinforcement bars, with a thickness of 4-25 mm.

Stainless steel reinforcement bars are typically used in the reinforcement of tunnel walls and bridges and in marine applications. The use of stainless steel reinforcement bars has increased significantly in recent years, especially in countries where road de-icing salt is applied. In special applications such as bridge structures, which are subject to high stress from both humid and chloridic atmospheres and mechanical and chloridic stress, reinforcement bars are made of highly corrosion resistant steels, containing molybdenum.

1.3 Use of stainless steel in construction
The construction industry mainly uses austenitic stainless steels, as their corrosion resistance, strength and formability are best suited to building applications. Ferritic grades are used for interior cladding, and specialist products are available for roofing.

In applications subject to severe atmospheric stress, and in structures for which lightweight architectural solutions are sought, stainless steel is often the only alternative. The main selection criteria favouring stainless steel are its ease of use and low need of maintenance. Structures can be left visible and, with stainless steel, contemporary and highly effective designs can be achieved.

Environmental values and the protection of the environment have made long-term durability and total life cycle cost, as well as the environmental impact of structures, important material-selection criteria. Life cycle philosophy (LCA, LCC) favours the use of structural materials, such as stainless steel, which resist both mechanical and atmospheric stress and are easy to maintain.

Buildings
In buildings, stainless steel is most commonly used on façades and interior surfaces, in stair structures, balconies, doors and lifts, as well as in various supplementary structures such as canopies, hatches and balustrades. The use of stainless steel in load-bearing structures is fast increasing.

The construction industry uses about 12% of the total global production volume of cold rolled stainless steel and about 5% of that of hot rolled stainless steel. The amount of stainless steel used for building purposes varies from one country to another. The use of stainless steel is rapidly increasing in European countries. In some Asian countries, such as Taiwan and Japan, building and construction may account for more than 20% of total stainless steel consumption. /2/

Load-bearing structures
Austenitic steel possesses better strength properties, both at room temperature and in a fire, than structural carbon steels. There is currently much research being carried out into stainless steel’s load-bearing and fire-resistance properties. Some European countries approve stainless steel structures corresponding to fire-resistance class R30, without any separate fireproofing /3/. The development and renewal of standards concerning the use of stainless steels in structures has focused on the use of high-strength materials when preparing dimensioning codes for both room temperature and fire situations. The development of dimensioning standards for stainless steel has also involved extensive European co-operation.

Hollow sections for construction applications are made of stainless steel with rectangular and square cross-sections, using both hot and cold rolled steel. Usually, the most common austenitic steel grades are used. Typical applications include not only load-bearing frame structures for buildings, but also frame structures for canopies and balconies, glass façade frames and various supplementary structures. Rectangular hollow sections for frame structures are available in wide variety of exterior dimensions and wall thicknesses. In column structures or visible horizontal girders and lattices that must be particularly strong, maximum dimensions are used. In lightweight structures, stainless steel rectangular hollow sections make it possible to achieve high load-bearing capacities.

Surface structures
In the building trade, light-gauge stainless steel sheet products are mainly used as cladding sheets, cassettes, mouldings and roofing. Choice of stainless steel will centre on issues related to appearance and cleaning. The surface of light-gauge sheet can be polished in various ways, or patterned, and sheet can be straight, perforated or profiled. The steel can also be coloured or painted. The use of stainless steel nets, of varying thickness, in supplementary structures and balustrades, for example, has increased. Stainless steel’s excellent corrosion resistance also makes it ideal for applications subject to severe atmospheric stress.

Supplementary structures and building components
Factors such as ease of cleaning and maintenance, as well as the excellent strength and rigidity required of slim structures, argue for the use of stainless steel in entrances and glass structures. Fasteners used in glazing are also often made of stainless steel. With no need for coatings, costly painting is eliminated, as is repainting, with its attendant disruption and protective measures. Where stainless steel is used in entrances, the doors, balustrades and fixtures are often also made of the same material. Stainless steel fixtures, already very popular, are constantly gaining popularity.

Fasteners made of stainless steel are often used as masonry and concrete ties, and as fasteners in façade cladding systems and glass façades. Stainless nails and fasteners are also commonly used in wooden structures.

Stainless steel concrete reinforcement bars are used in structures highly susceptible to corrosion, such as bridges, tunnels and foundations. The use of stainless steel reinforcement bars has also become quite common in external wall elements.

Bridges and urban structures
Bridges have a long required service life. Typical applications of stainless steel in bridges include various composite structures, supplementary structures and wires, as well as slab reinforcement bars. When stainless steel reinforcement bars are used, the estimated service life of the deck of a reinforced concrete bridge is up to 75-100 years. Stainless steel can also be used in the fixing points of other road structures. Besides mechanical wear and atmospheric influences, factors contributing to corrosion included also road salting. In road maintenance, corrosion generates not only repair costs, but also traffic disturbances and delays, due to repair activities. These represent a significant cost. It is therefore advantageous to use stainless steel reinforcement bars, since tests show they resist high chloride content over several decades. Normal carbon steel reinforcement bars are known to require replacement much more frequently, because of corrosion.

Various harbour structures and piers are subject to stress levels similar to those of bridges. This not only applies to structures in direct contact with seawater, but also to shore structures susceptible to stress caused by chloride and humidity.

Stainless steel is commonly used in various street furniture, such as kiosks, bus stop structures and canopies, benches, flagpoles and street lighting units, as well as children’s playgrounds and litter bins. The soiling and graffiti risks to which urban structures are subject also point to the use of stainless steel. Cleaning costs for stainless steel surfaces are relatively low. No special tools or detergents are needed and all cleaning can be carried out using ordinary methods.

Fixtures
Another main area of application for stainless steel is in the supply and treatment of water. Stainless steel is used to manufacture taps, water pipes and various fixings, battens and fittings. The fixtures and supplementary structures of wet areas, such as sinks, cabinets and battens are also often made of stainless steel. Designers of kitchen and bathroom fixtures and furniture have both increased their use of stainless steel in recent years and come up with new applications, beyond just taps and sink units.

Stainless steel has found applications in buildings intended for leisure and sports activities, such as in the pool structures of swimming baths. It is also often used as a cladding material. Swimming pool accessories, such as railings, stairs, partition walls and children’s fixtures are, in practice, always made of stainless steel. Because high chloride content and humidity create extremely severe atmospheric conditions, steel used in swimming baths should mainly be of the molybdenum-containing. In other sports facilities, stainless steel is used to some extent as a structural and cladding material, for reasons of ease of maintenance and durability.

Steel equipment and surfaces are widely used in hospitals and other healthcare facilities. In electromagnetic medical applications, stainless steel is used as a protective material.

In public premises involving no special requirements, owing to the nature of their purpose, steel surfaces and fixtures are often favoured for the same reasons that apply to street furniture. By using a material that is resistant to damage and can be easily cleaned, vandalism can be minimised and the results of any damage readily repaired.

1.4 Material properties
The austenitic steels used in the construction industry possess certain special properties that need to be considered when designing stainless steel structures. Benefit can be gained from cold forming, which increases the strength of the steels. Austenitic steels are non-magnetic, although cold forming may cause slight magnetism. The heat conductivity of stainless steels is lower than that of other structural steels. Their higher heat expansion coefficient is a major consideration, particularly in the case of joints. The excellent strength properties of the material at high temperatures can be utilised in fire design.

Material selection
Factors influencing the selection of a suitable stainless steel grade for an application include the ambient conditions, the manufacturing process, the possible need for machining, and requirements concerning surface appearance and maintenance of the structure. During its service life, a structure will be subject to various forms of corrosion that can be controlled by correct material selection. Experience previously gained in the corrosion resistance of the different steel grades is regularly considered in structural design. The initial investment costs associated with certain stainless steel grades, however, may be quite significant, and the price of the steel relates directly to its corrosion resistance. The availability of stainless steel grades, and structural parts made of different stainless steel grades, must also be borne in mind. A designer should therefore know the grades available, and their properties.

When selecting stainless steel for a particular application, it is necessary to define the conditions, choose the grade suitable for those applications and verify the correct processing and manufacturing methods. The most relevant ambient factor is the possible concentration of halides (especially chlorides) and sulphur dioxide. The effect of the surroundings – for example the influence of the structural parts and materials in contact with the steel – must also be noted. Mechanical properties, requirements affecting the finished structure, ease of manufacture, product forms and surface quality are other factors to be considered.

A surface finish selected on the basis of the environment and the structure’s intended use will ensure long-term durability and good service properties. It will take into account such factors as ease of cleaning, scratch-proof properties or choice of matt or reflective surface. The selection of surface finish deserves special attention, as practical differences between various finishes are considerable.

There are clear instructions available for the selection of screws used in the fixing of different stainless steel grades. The screws’ corrosion resistance must be at least equal to that of the steel itself. /4/

After the most suitable steel grade has been selected for the application in question, selecting the fabrication processing methods ensures its long-term durability. The designer should also draw up instructions with regard to the equipment, materials and work methods used in the processing of the stainless steel. These are discussed in Chapter 4, under “Construction site techniques.”

Steel producers’ inspection procedures involve verification of product analysis, testing of mechanical values, verification of product dimensions and inspection of surface quality. When delivered, the steel is normally accompanied by a material certificate containing the analysis of the batch, the dimensions, the results of mechanical tests and the identification data. The manufacturer’s name, steel grade code, melting batch number and identification number are marked on every stainless steel item delivered. The manufacturer may also mark the dressing status of the sheet or coil, the rolling direction (if necessary), the nominal dimensions and the customer’s order number. More detailed instructions are available for the marking of prefabricated steel products.

Long-term durability
Provided stainless steel structures are carefully designed and the steel is correctly selected, treated and maintained, the theoretical service life of stainless steel structures can stretch into hundreds of years. A rough estimate of the success of the design and the durability of a structure can be made after a few years. A rule of thumb is that if there are no rust stains, indicating corrosion, in the first few years, there is little risk of corrosion later.

Stainless steel may be attacked by pitting corrosion, crevice corrosion, galvanic corrosion, stress corrosion cracking, general corrosion and intergranular corrosion. These corrosion types may occur either separately or in various combinations, depending on ambient conditions. /5/

Corrosion risks can be roughly divided into three levels, which depend on the materials, the type of corrosion and the ambient conditions. /6/ General instructions for material selection can be provided at risk levels 1 and 2. At risk level 3, structural design must be carried out under expert supervision.

- At risk level 1, no significant corrosion defects will occur over a 50-year design service life. No structural repair is needed, although aesthetic aspects may require some maintenance. In normal corrosion conditions, most stainless steels meet the requirements well.

- Risk level 2 involves a risk of pitting or crevice corrosion, that may require some repair during a 50-year design service life. This risk level applies to atmospheric conditions involving either a marine environment or chemical emissions from industrial processes.

- Risk level 3 involves various aggressive media, such as acidic chloride layers, which may cause structural deterioration as a result of cracking due to local stress corrosion. Service life, at this level, is determined by the choice of material and the probability of exposure to, and influence from, harmful media. Structures belonging to risk level 3 are found in, for example, indoor swimming pool atmospheres and applications susceptible to fire.

Environmental properties
The environmental impact of the manufacture and use of materials and products can be measured in terms of the amount and toxic effect of the emissions involved, as well as in terms of energy demand. The values and decision-making processes of consumers and companies today are based not only on traditional values, but also on environmental impact considerations. Environment-friendly products tend to be valued highly in selection situations. Legislation in recent years has also increasingly emphasised environmental values.

Stainless steel is mainly manufactured from recycled carbon steel and stainless steel. Using recycled raw material reduces the energy required for the manufacturing process, as well as reducing waste and emissions. Depending on the process route, 60-70% of the raw material used in the manufacture of stainless steel consists of scrap metal. The remaining 30-40% consists mainly of alloying metals.

Stainless steel itself is 100% recyclable. Thanks to the excellent durability of the material, however, product service life is extremely long. This reduces the consumption of natural resources and energy during the service life of stainless steel products, in comparison with that of products made from materials that wear out faster and need to be replaced.

Today’s stainless steel mills pay particular attention to emissions. All particles released during the manufacturing process, for example, are filtered and collected. Advanced environmental technology is an essential part of the state-of-the-art stainless steel manufacturing process.

The environmental impact of products and processes is often assessed using Life Cycle Assessment (LCA) methods, in which the environmental impact resulting from the manufacture, processing, use, logistics and final disposal of a product is assessed using specific default values in each case. From a Life Cycle Assessment point of view, stainless steel’s strengths include:
- its recyclability;
- its use of recycled raw materials;
- the relatively low energy consumption of the manufacturing process.

Life cycle costs
Life Cycle Costing (LCC) takes into account the costs of manufacture, use and possible re-use, and final disposal. Cost items are divided differently depending on the product. Often, the cost of manufacture represents only a very small part, yet decisions are often based just on such initial costs. From the end-user’s viewpoint, the correct approach would be to consider total life cycle costs.

The investment costs of structures can be divided into:
- design cost
- material cost
- production cost
- surface treatment and finishing cost
- inspection and testing cost.

The manufacturing cost of stainless steel structural elements can be significantly influenced at design stage. The most dominant factor in the market price of stainless steel is the steel’s grade. Another factor is the cost of the chosen finishing method. In frame structures, however, the material or surface finish selected does not usually make a great difference since, in most cases, it is not necessary to opt for the best grade. Noticeably more expensive grades are normally chosen because they possess high-strength and corrosion-resistance properties that will generate savings elsewhere.

While material cost may be quite high in the case of stainless steel structures, costs generated by the installation, joining and handling of the finished structure correspond to those generated by other building materials. Since no separate surface treatment is needed, the costs incurred at the construction site consist only of mechanical installation expenses. Inspection costs are low, because stainless steel surfaces do not require regular inspection, to determine the need for renewal.

The maintenance costs of stainless steel structures are very low. All materials require regular cleaning and occasional maintenance measures, but stainless steel is definitely one of the most durable and easy-to-clean.

As no surface treatment is needed, nor, therefore, any renewal of surface treatment, maintenance is also easy.

Stainless steel parts in concealed structures can go without maintenance for hundreds of years, in some cases. Provided the surface finishes are correctly selected and processed, and subsequently correctly maintained, the surface structures will last for an extremely long time, in present climatic conditions.

As a recyclable material, with an existing market, stainless steel scrap has a high residual value, after the service life of the building has expired. This residual value, however, has only a minor influence on total life cycle cost, due to the exceptional length of service. Life cycle cost is usually calculated, over the estimated service lifetime, either by valuing partial costs at their present value or by converting them into annuities.

1.5 Glossary
AOD method - Argon Oxygen Decarburisation – removal of carbon from molten steel using argon oxygen blowing.
austenite - Crystallised metal structure – non-magnetic iron alloy.
austenitic ferritic - Metal that displays both austenitic and ferritic crystal structure.
cast moulding - Casting into moulds (cf. continuous casting).
continuous casting - Casting of molten steel in a continuous process through a copper chill.
converter - Process equipment used, for example, in decarburisation.
double façade - A façade consisting of two layers, with an air gap between the inner and outer layer. Usually consists mainly of glass structures.
duplex steel - Commercial designation of austenitic-ferritic alloy.
edging - Bending.
environmental technology - Technical applications that promote the protection of the environment, usually aimed at limiting pollution and making more efficient use of energy.
ferrite - Crystallised metal structure – magnetic iron alloy.
ferrochrome - An alloy of chromium, iron and carbon, containing about 50% chromium.
heat treatment - Heat treatment or pre-heating at 1,000-1,300°C.
Life Cycle Assessment (LCA) - Analysis of the effect of a product, activity or industrial sector, over its lifetime.
Life Cycle Costing (LCC) - Method for assessing the cost of manufacture, use and final disposal of a product (or operation) over its lifetime.
Long term durability - The ability of a material or structure to resist mechanical wear, erosion and corrosion caused by atmospheric and ambient stress.
martensite - Crystallised metal structure – a hard material.
pickling (and passivating) - Chemical treatment for cleaning the surface of stainless steel, which removes iron oxides from the surface and creates the conditions for a homogeneous passive layer to form.
profiling - Forming strip or sheet into a desired shape (by bending).
rectangular hollow section - = structural hollow section A tubular section with a rectangular cross-section.
recycling - Re-use of the material of a product.
residual value - Commercial value of a product or material after disposal.
roll forming - Forming of steel strip using a set of rolls.
rolling (hot rolling, cold rolling) -- Use of compression and tension produced by rolls to make metal thinner.
stainless steel - Steel alloy containing at least 10.5% chromium and a maximum of 1.2% carbon.
18/8 or 18/10 steel - Stainless steel containing 17-19.5% chromium and 8-10.5% nickel.

1.6 Standards concerning stainless steel
EN 10088 is now consistently applied throughout Europe. Another relevant standard is the AISI and UNS standard, applied in countries outside Europe.

Listed below are the most common and important standards and design codes directly related to stainless steels and their use in construction. Separate standards, not included in the list, exist covering stainless steel fixings, the welding of stainless steels, etc.

EN 10088-1 Stainless steels - Part 1: List of stainless steels

EN 10088-2 Stainless steels - Technical delivery conditions for sheet/plate and strip, for general purposes.

EN 10088-3 Stainless steels - Technical delivery conditions for semi-finished products, bars, rods and sections, for general purposes.

EN ISO 3651-1 Determining stainless steels’ resistance to intergranular corrosion.

EN 10259 Cold rolled stainless steel wide strip and plate/sheet
Tolerances concerning dimensions and shape.

EN 502 Roofing products from metal sheet
Specification for fully supported roofing products of stainless steel sheet.

EN 508-3 Roofing products from metal sheet
Specification for self-supporting products of stainless steel sheet.

ENV 1090-6 Execution of steel structures
Supplementary rules for stainless steel structures.

ENV 1993-1-4, Eurocode 3: Design of steel structures
Part 1-4: General rules. Supplementary rules for stainless steels.

1.7 Bibliography
/1/ Euro Inox, “Guide to Stainless Steel Finishes”, Building Series, Volume 1
/2/ “Stainless Steel in Construction,” Meeting Proceedings. Outokumpu, Espoo 1998.
/3/ Steel Norm Card no. 10/1999, Fire technical design structures made of austenitic stainless steel, The Finnish Constructional Steelwork Association.
/4/ “Design Manual for Structural Stainless Steel,” 2nd edition, Luxemburg 2002, Building Series, Volume 6.
/5/ Euro Inox, “Handbook of Stainless Steel,” Materials and Applications Series, Volume 1
/6/ ENV 1993-1-4, Eurocode 3: Design of steel structures. Part 1-4: General rules. Supplementary rules for stainless steels, CEN 1996.

2 Stainless steel in architecture
2.1 The start of steel construction
The development of building materials has had a clear influence on the nature of structures and also, as a result, on the development of architecture. Major landmarks have been the industrialisation of iron manufacture, the invention of steel and the development of industrial steel manufacture.

The Iron Bridge, built in Great Britain at the end of the 18th century, was one of the first bridge-building projects based on the use of cast iron. In 1851, Joseph Paxton designed Crystal Palace, as a temporary exhibition building for the World Exhibition.

Libraries by Henri Labrouste, Paris, 19th century
In 1838-1850, the French architect, Henri Labrouste, designed the architecturally significant Bibliothèque Ste Geneviève to have a cast iron frame. In 1867, another library of considerable architectural value, the National Library of France (Bibliothèque Nationale de France), also designed by Labrouste, was completed in Paris.

Labrouste’s library buildings make use of natural light (in the reading rooms, for example), electric lighting not being available at that time – at least, not in its present form. Natural light enters the buildings through glass and metal structures, pleasantly illuminating the library’s interior.

Paris railway stations, late 19th century
The Gare du Nord station in Paris, designed by Jacques Hittorff and completed in 1864, is built on a metal frame. It is, perhaps, one of the most elegant stations in Europe, owing to the lightness of the structures and the abundance of natural light within the building.

The use of metal structures increased in the second half of the 19th century, especially for projects requiring large spans. Examples include the Gare du Nord, Gare de l’Est and Gare d’Orsay railway stations, in Paris, as well as several German railway stations and structures requiring bridges, such as metropolitan line no. 1, in Berlin.

In the 19th century, large structures, such as the libraries designed by Labrouste and the Paris railway stations , were constructed using iron. Steel, however, gradually increased in popularity, as steel-production statistics show: 74,000 tons in 1820, 246,000 in 1850 and one million tons in 1882.

The broadening of steel applications.
The use of metal expanded to include all kinds of structures, such as residential houses, commercial premises, department stores and conference facilities, etc. This is clearly illustrated by the production of the Belgian, Viktor Horta, at the turn of the 20th century. Horta’s architecture is characterised by light, slender structures. Steel structures used together with natural stone and brick typify his production at that period.

In the construction trade, steel rose to a significant position in less than a hundred years. This was made possible by the development of iron and steel production methods and the mastering of the structures made from these materials. Naturally, new architectural concepts entailing the use of metal structures were also required.

2.2 Stainless steel in construction and architecture
Stainless steel was patented in Germany at the beginning of the 20th century. It was also developed at the same time in England. At first, the material was mainly used by the engineering industry in the manufacture of machines and equipment, and for medical instruments, etc. Then it was gradually introduced into the construction industry.

Chrysler Building, New York, 1930
The Chrysler Building, in New York, in which stainless steel plays a visible role, is one of the most significant buildings of the 1920s and 1930s. When completed in 1930, it was the tallest building in the world and made the designer, architect William Van Alen, an overnight celebrity. Today, it remains one of New York’s landmarks. The Chrysler Building represents pure, well-implemented art deco. The building’s renown, however, is really based on the expressive, art deco design of the top section, which is covered with stainless steel.

Arne Jacobsen – 1950s and 1960s
The architecture of the Dane, Arne Jacobsen, is characterised by his way of creating whole building environments in one unified style. Jacobsen’s office also designed all the furniture and small objects for the buildings, all representative of the detailed, small-scale design style typical of even his grandest projects.

Arne Jacobsen used stainless steel in many well-known designs, such as his cutlery and coffee pots, as well as in the interior of buildings (in stair rails, for example) and also to some extent in external cladding elements. The furniture and small objects originally designed for architectural projects have started to live a life of their own, outside the buildings. Essential examples of classic 1950s and 1960s modernism, most of them are still on sale, throughout the world.

Lloyd’s of London, 1970s
The Lloyd’s of London building was constructed on the basis of English architect Richard Rogers’ winning entry in a restricted competition. The main aim of the design – to provide clarity in the interior spaces – is achieved by locating the staircases and building systems on the outside of the building. Stainless steel is used as cladding on the technical units. The building blends excellently into the City of London townscape. At close range, it creates an effective contrast to the surrounding blocks. The controlled, sculptural shapes of the technical parts of the building make an unforgettable impression, in the tight urban space.

Stainless steel is clearly a significant material in the external architecture of Lloyd’s of London. The frame of the building, made of reinforced concrete, is built using prefabricated parts.

National Library of France, 1990s
The new National Library of France (Bibliothèque Nationale de France), designed by architect Dominique Perrault on the basis of a winning competition entry, was completed in Paris in 1995. It was one of the most significant construction projects of François Mitterrand’s presidency. The building was widely acclaimed in the world press, with discussions of, for example, its space concept, architectural language and connections with classic modernism (such as Mies van der Rohe’s architecture during his stay in America). There was also wide discussion of the technological character of the building, including such features as the way in which books are transferred from storerooms in the towers to the reading rooms.

The library may also be discussed in terms of the materials used and implementation methods adopted. The reinforced concrete frame of the building is of very high-quality construction. The shell structure consists mostly of tropical wood, glass and stainless steel, some of them higher alloyed grades. Stainless steel is also very visibly present in the interior spaces, with, for example, woven steel nets on the walls and ceilings, combined with natural-colour reinforced concrete, textiles (such as red wall-to-wall carpeting in the entrance lobby) and reddish tropical wood.

The external shell of the library is constructed using three materials. One is stainless steel, used in various finishes, as matt surface plates and woven lattices. The building mass also incorporates trees and bushes, surrounded by stainless-steel wire frames. In fact, the central external space features a small, forest-like, tree feature, surrounded by the tall public facilities of the library and approached directly by the main entrance passage. The consistent use of high-quality materials in the external shell and the building’s highly effective division of volume combine to create a convincing overall result.

The number of woven stainless steel components used in both the external and internal spaces of the library is considerable. The steel parts are stainless steel components used by industry, such as paper-machine wire mesh and woven cables. Used here in a public facility, they reflect the collage technique that Perrault also used in his earlier works.

Perrault’s office also designed the library’s individual lighting units, the reading room furniture and the bookshelves, etc. The steel frame armchairs in the public lounges are of Danish design, and there is a clear correlation between the environments created by Perrault and those of Arne Jacobsen. Both are characterised by a unique sense of innovation and by consistency of solutions. Contrary to the modernism of the 1950s and 1960s, the National Library of France represents a more recent architectural approach. Its multiplier impact is evident all over Europe, where the use of woven stainless steel has expanded.

Berlin velodrome and swimming bath, 1990s
The Berlin velodrome and swimming bath complex, designed by Dominique Perrault, on the basis of a winning 1992 competition entry, was completed in 1998. The velodrome is a round, low mass, adjoining the low, rectangular swimming bath. The geometrical shapes of the structures are planted lower than the surface of the surrounding street network. For the most part, only the entrance stairs and grounds, planted with apple trees and located at the roof level of the structures, are visible in the town space. Natural light enters the velodrome and the swimming bath through steel roof structures entirely covered with woven stainless steel net.

Ludwig Erhard Haus, Berlin
This building, designed in 1994-1998, houses the Berlin Stock Exchange, the Chamber of Commerce and the Federation of Industrialists. Located in the Charlottenburg area of the city, it is the communication and services centre for Berlin’s commercial and industrial communities.

Architect Nicholas Grimshaw designed the building on the basis of a winning entry in a restricted competition. The basic idea of the design was a low solution that would complement the townscape, featuring a suspended structure for the central building mass. The building combines the traditional modern architecture of the office section with a highly structural, organic appearance and careful attention to ecological requirements.

Stainless steel used in the external shell, and in the cast cladding of the steel arches at ground level, gives the building an extra dimension of interest.

The designer had to adapt eye-catching architecture, the requirements of new technology and the needs of the building’s diverse activities to the existing environment. The load-bearing structure consists of 15 steel arches, from which the top nine floors are suspended. This approach maximises the available free space. The elliptical steel arches were industrially prefabricated. The street façade is a light, separate structure, supported on steel arches. This makes the building’s central mass resemble a suspension bridge structure.

The building is equipped with natural ventilation and its atriums serve to regulate ventilation in the workspaces. A solar control system, incorporated in the façades, reduces the need for artificial lighting.

The bulk of the office facilities, representing some 18,000 m2, can be found on the 2nd-9th floors, while the 1st floor contains various conference, exhibition and office facilities. The Stock Exchange dominates the ground floor, along with a 1,200-m2 restaurant and a shopping arcade. The first basement floor contains parking facilities, plus a conference and lecture room, and the 2nd basement floor provides more parking space. The two atriums of the building receive natural light through the shell structure and let light into the offices and workrooms. The lifts to the upper floors run inside the atriums. Steel bridges, running longitudinally on the 2nd-9th floors, connect the spaces separated by the atriums.

Sony Centre, Berlin
In recent years, quite a few office complexes, designed by renowned architects and displaying interesting applications of stainless steel, have risen in Berlin. The Sony Centre, completed in 2000, on Potsdamer Platz, in the main business district, contains not only offices but also commercial premises. The mass division of the building complex, designed by Helmut Jahn, is an example of space diversity. The façades of the building block are mainly constructed of stainless steel and glass, with stainless steel used as sections, plates, corrugated sheets and woven surfaces. The Charlemagne building in Brussels, designed by the same office, can be described as being, in spirit, a much more enclosed administrative building, while Berlin’s Sony Centre opens up in many directions, making it an easy-to-access block with a versatile space solution.

2.3 The diversification of stainless steel applications
Examples of stainless steel applications in architecture reflect the broadening of the material’s applications in construction. The use of stainless steel has increased considerably, its applications having became more diversified in significant European building projects of the 1990s. Many of the applications involve shell structures, such as façades and façade components. Stainless steel has also become a material for load-bearing structures, such as stainless steel frames and concrete reinforcement bars. Stainless steel surfaces have traditionally been bright, either ground or polished, but matt surface stainless steel is gaining popularity in façade structures.

The use of woven stainless steel surfaces in the interior and exterior spaces of buildings is a completely new phenomenon. In external spaces, they are mainly used in cold structures, such as wind shields and sunscreens. Lately, façade components have also been made as cast stainless steel structures. An example is Berlin’s Ludwig Erhard Haus building, completed in the late 1990s, which has a prefabricated steel frame and a stainless steel envelope.

Less than a hundred years after stainless steel was invented, its properties are being exploited for all building parts, from cladding to load-bearing and supplementary structures.

2.4 Residential buildings
In the internal spaces of residential buildings, stainless steel is mainly used in kitchens and wet areas – in sink units and stove hoods, for example. The material is also becoming more popular in household appliances and for applications such as cupboard skirtings, door fittings and fireplaces.

In the shell structures of residential buildings, stainless steel’s uses include balcony structures, down pipes and external door sills. Stainless steel has also found applications in the lifts of residential buildings. In Finland, for example, balconies and lifts are now built using prefabricated stainless steel elements. Other building parts available in stainless steel include double-walled chimneys, for exterior use.

In house building, stainless steel’s ease of maintenance makes the material ideal for fence posts, load-bearing structures and, particularly, cold structures. Stainless steel load-bearing structures, using various surface treatment methods, can also be left visible, thanks to the material’s aesthetic appeal.

2.5 Public buildings
Stainless steel began to be used in the structures and buildings of public transport services in the 1960s and 1970s. Its long service life and ease of maintenance make stainless steel an ideal material in structures designed to serve large numbers of people, such as railway and underground stations, bus shelters, passenger ship terminals and airports.

Helsinki Metro (underground system)
The planning of Helsinki’s underground system started towards the end of the 1960s. Its first trains ran in 1982. The Helsinki City Underground System Office, set up to plan and construct the system, engaged various architectural teams and engineering offices to design the stations. The work also covered designing so-called continuous structures, such as the signs and fixtures, as well as the trains. These designs were applied consistently throughout the system. The choice of higher alloyed steel for the stations’ external doors, lifts, column shields, fixtures and signs was based on issues related to maintenance and the corrosive urban atmosphere.

Helsinki-Vantaa Airport
Helsinki-Vantaa Airport was extended in the 1980s and 1990s. Architectural planning for the project was carried out by Architects Pekka Salminen. The second phase of the central terminal, completed in 1999, won the Steel Construction Award that year. Stainless steel components are abundantly used in the terminal’s customer service areas, alongside glass, painted steel and wooden surfaces and the natural stone used on the floors.

Stainless steel is mainly used in fixtures and furniture, balustrade structures, lifts and, to some extent, in façade structures.

Line M14, Paris Métro (underground system)
The interior and cladding structures of the new M14 Paris Métro line, of stainless steel and glass, emphasise the rejuvenated Paris of the 21st century. The new structures of this line, running from Madeleine, in central Paris, to the National Library, blend naturally into the street surroundings. They exemplify advanced implementation techniques.

Museum of Science and Industry, Paris
The Museum of Science and Industry, in the Parc de la Villette, Paris, was opened in 1986. This building, designed by architect Adrien Fainsilber, was built utilising the reinforced concrete frame originally intended for the never-completed Paris central abattoir. Its roof slab is supported by massive steel beams. The long façades are made of ground stainless steel, blue-painted steel, glass and natural stone. The frame structure and glazing fixings of the greenhouse facilities on the southern façades are also made of stainless steel. The cladding on the globe-shaped wide-screen cinema (La Géode) adjoining the museum, on the other hand, is bright annealed stainless steel. This produces a mirror-like effect. La Géode is a conscious flashback to the utopian globe shapes of 18th century architects Bouleé and Ledoux.

La Villette, Paris
The 30-hectare Parc de la Villette, in the area of the former central abattoir, has been turned into one of the world’s most interesting park complexes. This recreational facility and tourist attraction, called “the park of the 21st century” by its designer, includes sports facilities, music pavilions, various park displays and aquatic themes, such as a canal. A 200-metre long gallery, running through the park, provides shelter in rainy weather.

The park was created on the basis of a plan drawn up by architect Bernard Tschumi, consisting of 30 separate pavilions (folies), mainly built of steel, each representing a different theme, plus other small-scale metal structures. Apart from steel, other metals, such as stainless steel and aluminium, are used.

Notre Dame de l’Arche d’Alliance church, Paris
The shape of this church, built in 1997, in the 16th arrondissement of Paris, represents a wooden, biblical Arc of the Covenant. The simple geometrical shape, an equal-sided cube, symbolises the concept of the Deity. Standing off the ground, on columns, the cube is surrounded by a three-dimensional metal frame. This frame serves as an intermediary element between the spiritual and the earthly space.

The church is impressive in its simplicity, both inside and out. Its external walls are clad with warm-brown coloured laminate boards, resembling a wooden wall. The wall’s surface is covered with texts. The stainless steel frame, the stainless steel bell tower and the geometrical shape of the building make the church a lively small-scale urban monument.

The church was designed by Architecture Studio – a company known for having designed the European Parliament building.

2.6 Industrial buildings
The most extensive use of stainless steel has been in industrial buildings. Its use in this context also began earlier. The process industries use stainless steel in machines, equipment and transport piping, due to its resistance to aggressive media. Heavy users of the material include the paper and pulp industry, power plants and the food industry. In dairies, for example, stainless steel is the main material for a particularly wide range of equipment.

Industrial architecture has undergone a change in the 20th century, as companies have come to pay more attention to the image conveyed by their facilities and production plants. In Great Britain, architects who have developed an architecture that utilises technically advanced structural and engineering solutions include Richard Rogers, Norman Forster and Nicholas Grimshaw.

The Western Morning News headquarters building, designed by Nicholas Grimshaw, houses the newspaper’s editorial offices and production facilities. This representative example of high-tech architecture, in Plymouth, was completed in 1992. The building is very open to the outside, with cast structures made of steel and stainless steel on the façades. Other buildings by Grimshaw include the extension to London’s Waterloo station , and the Berlin Stock Exchange, in which stainless steel is used in the shell structures.

The OCAS research centre for the application of steel, near Ghent, Belgium, was built in 1989-1991. This steel building is intended both to demonstrate and to make a statement. The tall wings, containing engineering testing facilities, have stainless steel cladding structures. The building was designed by the Brussels-based architects, Samyn & Partners.

2.7 Office buildings
Stainless steel’s relatively low maintenance requirements and long service life, and the image values partly based on these characteristics, have greatly increased the material’s popularity for office-block use. A good example is the administrative building of Lloyd’s of London, completed in 1984, in which stainless steel is used for the external cladding.

Aspotalo building, Helsinki, 1990
Aspotalo, in Helsinki, completed in 1990, is the first office block in Finland whose façade cladding consists solely of a higher-alloyed stainless steel. Located on the coast, the building is thus in one of the most demanding atmospheres.

The sunscreens, also stainless steel, add to the liveliness of the façade mass. The building was designed by Architects Jan Söderlund & Co., with architect Eero Eskelinen as main designer.

Charlemagne, Brussels, 1998
In 1998, the Charlemagne office block in Brussels was renovated, mainly in preparation for use by the European Union. The renovation project concerned the entire building, and the building’s overall appearance was considerably altered. The new façades are mainly of glass and stainless steel, using steel plate processed with a turret punch. The ground stainless steel used alongside glass in the large façades is highly uniform, thanks to its thickness, and gives the building credibility in the townscape. The project’s main architect was Helmuth Jahn, of Chicago. Architecture studio H. Hontirs supervised the project in Belgium.

DG Bank, Berlin, 2000
The head office of DG Bank, Pariser Platz, Berlin, designed by Frank Gehry, was completed in 2000. This 19,000-m2 building contains offices, a casino and a lounge for cultural events, and also houses a residential section. The façade is of sandstone – which is also the material of the adjacent Brandenburger Tor. The large-scale windows and doors of the façades are stainless steel.

The façade facing the Pariser Platz is a simple rectangle. The size of the various openings on the façade, however, hints at the expressive nature of the building. Large-scale openings open up the Berliner façade. The opposite façade of the building undulates, in a sculptured manner. Gehry has used the same theme in other buildings. In a sense, the façade’s overall appearance can be said to be based on Byzantine architecture. The basic architectural approach and the scale, however, create an impression of a huge, pleasing sculpture, with a functional purpose.

Double façades
Office buildings with a so-called double façade became increasingly popular all over Europe, and notably in France, Belgium, Germany and Finland, in the 1990s. The use of a double façade is often justified by the energy-consumption and sound-insulation benefits that can be obtained.

The outer glass layer is often constructed using stainless steel profiles and fasteners.

3 Building parts
3.1 Load-bearing structures
Stainless steel has not been greatly used in load-bearing structures of buildings, but can be seen to be gaining popularity in this field. Stainless steel frames are starting to be used, particularly in buildings with special requirements in terms of strength, ease of maintenance, fire resistance and hygiene. As an example of long service life, the National Archives of Canada Preservation Centre, in Quebec, has a total design service-life expectancy of 500 years. The building, completed in 1998, was designed by Blouin Ikoy, with architect Ron Keenberg as main designer, on the basis of a winning entry in a 1991 national architectural competition. The archives section of the building is surrounded by a kind of large-scale double façade, whose steel structure, complete with load-bearing frame, is of stainless steel. The area between this structure and the archives section also serves as a public space. The materials used in the building have different design service lives.

The European projects described below use stainless steel not only for considerations of long-term durability and fire safety, but also for its high image value, ease of processing and wide range of surface finishes.

In the extension of the Louvre museum, designed by Ieoh Ming Pei, the load-bearing space structure of the glazing on the entrance pyramid is made of stainless steel. The external shell is constructed in glass and aluminium. The airy entrance to the extension, which mainly consists of underground space, is an essential element of the museum and has become one of the new symbols of Paris.

La Grande Arche stands on the extension of the Avenue des Champs-Elysées, in La Défense, on the outskirts of Paris. The Dane, Otto von Spreckelsen, won the international architectural competition, and became the building’s main designer. He had to resign before the building was completed, however, for health reasons. French architect, Paul Andreu, known as an airport designer, carried out the supplementary design. Andreu designed the panoramic lift, made of stainless steel, in collaboration with structural engineer Peter Rice. La Grande Arche was completed in 1989.

The architecture of the Notre Dame de l’Arche d’Alliance church, in Paris, is based on a dialogue between the frame that surrounds the church and the cube of the church within. In the town structure, the church serves as a kind of a catalyst, uniting the somewhat indefinite town space. The building impresses, in this environmental context, despite, or perhaps because of the slender structures. Its stainless steel frame is part of the load-bearing structure and an essential part of the church’s architecture.

Villa Inox was built for the Finland’s Tuusula Housing Fair, in 2000. The house’s load-bearing frame was prefabricated in engineering works, using stainless steel. The frame of the residential part of the house is a warm structure, which has been left visible. The use of a prefabricated frame structure brought construction time down to 3 months.

The load-bearing frame of Bergianska Trädgården, Stockholm, is built exclusively in higher alloyed steel, partly polished, partly painted.

3.2 Shell structures
Façades
In the 1990s, the popularity of stainless steel in façade structures increased. This was largely due to stainless steel’s corrosion resistance, which is a significant factor in urban and marine atmospheres. Atmospheric pollution in urban centres is, in fact, the most important reason for the use of higher alloyed stainless steel as a cladding material.

Other factors encouraging the use of stainless steel include its material properties, its refined appearance (which opens up the possibility of varied effects) and the formability of the surface.

In the 1960s and 1970s, the use of stainless steel in façade construction was mainly in the form of ground surfaces. In the 1990s, façades became livelier in appearance. It became common to use a greater variety of surface finishes, such as matt and coloured finishes, and cast structures. Various profiled forms of stainless steel sheet were also launched, such as cassettes, corrugated sheets and nets.

Towards the end of the 1990s, double façades constructed in steel and glass became popular in Europe, including Finland. Stainless steel is also used in double façades.

Façade glazing systems have also developed. Cast stainless steel fixings have gained in popularity, particularly in office blocks and public buildings.

Roofing
Stainless steel has a long tradition as a roofing material, as New York’s Chrysler Building, built in 1930, bears witness. The use of seam-welded stainless steel roofing began in Scandinavia and the rest of Europe in the mid-1960s. At about the same time, stainless steel began to appear in traditional standing-seam roofing in Central Europe.

Examples of Finnish buildings with seam-welded stainless steel roofing include the head office of an industrial group, in Herttoniemi, Helsinki, where the marine atmosphere dictates the use of specific materials, and Rovaniemi Airport, in the north.

La Géode, showpiece of the Museum of Science and Industry, is a geometrical, globe-shaped body, with a circular cinema screen. The structure’s cladding consists of 6,500 triangular, stainless steel sheets. La Géode is reminiscent of the utopian globe shapes of 18th century architects Bouleé and Ledoux.

3.3 Supplementary structures
The physical properties of stainless steel make it an ideal material for supplementary structures, such as façade components, balconies, rainwater drainage systems, staircases, balustrades, flues and mechanical engineering pipes. In external structures, stainless steel is mainly used for its excellent corrosion resistance. Fire safety and the material’s new, improved load-bearing properties are other important factors.

Its versatile surface-finish possibilities, in particular, make stainless steel also well suited to interior cladding use. Ease of cleaning and maintenance, as well as the high-quality appearance, have led to stainless steel being used extensively in environments designed to serve large numbers of people, such as the internal facilities of the Helsinki Metro. Helsinki-Vantaa Airport is a late-1990s example of a carefully considered combination of stainless steel, coated steel and wood surfaces.

3.4 Fixtures and furniture
Stainless steel has traditionally been used in premises where important criteria include hygiene, ease of cleaning and excellent corrosion resistance. Institutional kitchens, dairies and hospitals have thus taken advantage of stainless steel’s properties since the 1950s and 1960s. Stainless steel sink units for home use started to appear at the same time. In the 21st century, prefabricated, detachable kitchen units have become popular, particularly in Central Europe and the United States. Stainless steel is also rapidly evolving from being simply a worktop material into being a cladding material for fixtures and, in particular, kitchen appliances and equipment. It is also highly suitable for door fittings, cupboard skirtings, wet-area wall cladding and so on.

Metal furniture for the home, the office and public premises has been around since the 1920s and 1930s. Such furniture is usually made of chrome-plated or painted steel. Stainless steel is now also making its mark in this field.

3.5 Street furniture
Street furniture means small-scale, independent, functional structures incorporated into the urban space. Approaches to their design and fabrication are constantly evolving, and these objects vary from one country and, indeed, one town to another. Street furniture, often batch-produced, and manufactured in significant quantities, can also include unique items, designed for a specific purpose. It can have just one function, or be a combination of structures with several functions.

In the Place Vendôme, one of the most important Parisian squares, traffic is separated, today, by stainless steel bollards. This carefully proportioned square was designed by Jules Hardouin-Mansart and built by Louis XIV, in the 17th century. Delicately executed, the buildings surrounding the square are only four storeys high, and thus rather low in relation to the size of the square. The square’s interplay of materials, from the natural stone of the buildings to the modern, granite surface and the stainless steel bollards (of varied height), seems to bring out the sense of history and atmosphere. Stainless steel, used for small-scale, repeated elements, both discreetly complements the original square and enhances its practical aspects. Pierre Prunet was the main designer for the renovation project.

In town centres, stainless steel is often used for small-scale structures. The material is highly versatile. It is easy to maintain, has a neutral tone and is available in surface finishes of different reflectivity. Being highly corrosion resistant, its maintenance requirement is low.

4 Load-bearing structures
4.1 Structural design
Load-bearing structures are predominantly made of austenitic steels. The basic austenitic materials include 1.4301 (X5CrNi18-10) and the more corrosion resistant grade 1.4401 (X5CrNiMo17-12-2). If a structure involves a significant number of welded joints, a steel grade with lower carbon content would be suitable, such as 1.4307 (X2CrNi8-9) or 1.4404 (X2CrNiMo17-12-2). Austenitic-ferritic alloys are used in applications requiring excellent corrosion resistance or high strength. The most common austenitic-ferritic grades include 1.4362 (X2CrNi23-4) and 1.4462 (X2CrNiMoN22-5-3).

Load-bearing structures are normally built using rectangular hollow sections. The load-bearing capacity of a structure can be very high when sections of maximum dimensions are used. The work-hardening tendency of stainless steel during cold forming can be taken into consideration at design stage. Today, high strength stainless steel hollow sections are available, which owe their high yield strength and excellent load-bearing capacity to cold forming. This increases load-bearing capacity by 60%, and can thus save 20-60% in material consumption.

Design standards
The design of load-bearing structures is covered by Eurocode 3, Part 4, “Supplementary rules for stainless steels” /1/.
The “Design manual for structural stainless steel” /2/ was used as a source document in preparing the Eurocode standards. It is therefore a good reference document for more detailed background information. For export projects, in particular, helpful information can also be found in the German “Allgemeine bauaufsichtliche Zulassung” /3/ and the American “Specification for the design of cold-formed stainless steel structural members” /4/.

Further assistance concerning the use of stainless steels in special applications, such as in the load-bearing structures of swimming baths and spas, in water treatment plants and in concrete reinforcement bars, is available from the following information sources:
- Informationsstelle Edelstahl Rostfrei
- The Nickel Development Institute
- The Steel Construction Institute
- The International Stainless Steel Forum
- The Stainless Steel Information Center
- Australian Stainless Steel Development Association

Eurocode 3
Part ENV 1993-1-4
This standard applies to austenitic and austenitic-ferritic stainless steels. In addition, the Annex to the standard presents temporary design guidance for ferritic stainless steels. The basic assumption of the standard is that Eurocode 3 Part ENV 1993-1-1, for general structural steels, and ENV 1993-1-3, for light, thin-gauge members and sheeting, also apply to stainless steels, unless otherwise specified in the standard. The need for supplementary rules is mainly due to the differences in the mechanical properties of the materials. Owing to these differences in design rules, design software developed for general structural steels should be used with caution.

The most important difference between structural stainless steel and general structural steel is their stress-strain behaviour (Figure 4.1). General structural steel will typically display linear elastic behaviour up to the yield limit, while the stress-strain slope of stainless steel is typically curved.

Yield limit is the design basis used for general structural steels, but for stainless steels, stress corresponding to the 0.2% permanent elongation obtained in the tensile strength test is used. The stress-strain curve of general

Structural steels shows a yield plateau after the yield limit, while most stainless steels show pronounced work-hardening behaviour. The ratio between ultimate and yield strength is also usually higher with stainless steels than with general structural steels.

In standard ENV 1993-1-4, stainless steels are divided into nominal strength classes on the basis of design strength. Normal stainless steel EN 1.4301, for example, is in strength class S220, the so-called acid resistant steel EN 1.4401 in strength class S240 and duplex steel EN 1.4462 in strength class S480. The standard cannot be applied to steels whose design strength exceeds 480 N/mm2.

Structural design using stainless steels follows the same principles as those applying to general structural steels. There are, however, some differences:
- magnitude of the modulus of elasticity
- calculation of deflection in serviceability limit state
- cross-section classification of profiles
- calculation of flexural buckling
- calculation of torsional buckling
- calculation of shear strength
- design of bolted joints
- design of welded joints

ENV 1993-1-4 also lists the strength values of cold-formed plates. According to the standard, however, work-hardening characteristics can only be utilised if verified by tests, and strength values in a work-hardened state must not be applied to welded structures, unless they can be verified by means of tests.

Fire design
Austenitic stainless steel maintains its strength and elasticity well at higher temperatures, which makes the material ideal for load-bearing structures subject to specific fire resistance requirements. Some European countries have taken these into account in their National Application Documents.

The fire design of structures incorporates estimating fire development and calculating the structure’s temperature and structural strength. Structural design can be based either on a standard fire or on estimated fire development. The guidance presented in the Steel Norm Card /5/ can be used in both design methods. In design based on standard fire, a fire resistance time of up to 30 minutes can often be achieved with non-fireproofed structures, provided the design is correctly carried out. In design based on estimated fire development, longer fire resistance times can often be achieved. This essentially depends upon the building’s fire load, the growth rate of the estimated fire, and the model of the fire situation.

Stainless steels often find economical application in structures where coatings are undesirable, owing to factors such as appearance, risk of corrosion, maintenance cost or maintenance-related disruption. Such applications include external structures, façades, balconies, double façades and glass-roofed spaces. The low emissivity and heat conductivity of stainless steels can also be an advantage in compartmented structures.

Special features
Stainless steels possess certain special features worth recognising, although these rarely influence structural design.
- Owing to the material’s nonlinear stress-strain behaviour, minor permanent deformation of the structure is possible after the load has been removed, depending on the strength of the material. In tension members, maximum permanent deformation of the structure in a serviceability limit state may be 10-20% of the elastic deformation. In flexural members, permanent deflection is usually only a fraction of this.
- Stainless steels may display creep behaviour, at stress levels that exceed the design stress in serviceability limit state. Pre-tightened bolted joints, for example, are therefore not recommended, as the pre-tightening force is often very close to the yield strength of the bolt material.
- Within the 20-100°C temperature range, the design strength of stainless steels decreases considerably faster than that of general structural steels.
- The temperature coefficient of linear expansion is usually 1.5 times higher than that of general structural steels. This factor should be considered in the design.
- Many stainless steel grades have good impact toughness against brittle failure, which makes them also suitable at very low temperatures.
- Because of stainless steels’ work-hardening properties, structures will absorb a lot of energy in plastic deformation. Stainless steels are therefore also highly suited to structures subjected to impact or explosion loads.

4.2 Prefabrication
Stainless steel is easy to process in the manufacture of structures and components, but certain of its special properties ought to be borne in mind. The most significant of these is corrosion resistance, which must always be maintained. It is also important that the surface appearance is not changed or damaged during the manufacturing process, as finished stainless steel structures are normally neither painted nor treated.

In selecting the manufacturing method for stainless steel structures, attention should be paid to the following factors:
- the dimensions and quantities of the finished structural parts
- joining methods
- post-manufacture need for surface treatment or repairs to the surface finish
- requirements of parallelism for the surface finish
- maintenance of corrosion resistance
- the desired shape and size of the finished structure
- tolerance requirements
- structural requirements
- costs

Cutting techniques
Profile cutting of stainless steel can be carried out by mechanical cutting or perforation, or by plasma or laser cutting. If straight edges are required, the cutting tool is used in the same manner as in perforating. In water-jet cutting, the fluid is used to direct mechanically abrasive particles to a single point, at high speed. The advantage of this method is that the cutting surface does not become hot or damaged, but maintains all its properties. In the plasma arc cutting method, electrically charged particles move at high speed and at high temperature. The drawback of this method is that the heat damages the steel being cut. Laser cutting is a precision method that minimises the heat-affected zone, leaving the properties of the material unchanged.

Forming techniques
Thin-gauge sheet can be mechanically formed by roll forming or by edging with a brake pressing tool. In the roll forming process, steel strip is fed through a set of several cylindrical tools that gradually form the steel web into the desired profile. Roll forming is an economical manufacturing method for large batches. In edging, the thin-gauge sheet is pressed between formed tools. The length of the structures that can be produced by this method is restricted by the size of the tools. In addition, the method is slower than roll forming. Thin-gauge sheet can also be bent into a curved shape using bending tools.

Manufacturing methods based on material deformation will stretch the material, causing its thickness to change. The stretch/draw forming die can be matched or single. An elastic material, such as a rubber pad, can also replace one side of the die, so the elastic surface will distribute the pressing force evenly over the surface of the metal sheet. In stretch forming, straight, thin-gauge sheet is formed into a curved shape. The sheet is placed on the forming tool and pressed at its edges into the desired shape. Circular plates can also be formed by a method using a spinning motion.

Bending hollow sections and other prefabricated structures is more complex than forming sheet products, since it involves risk of deflection, wall thinning and stress. Small-diameter tubes can be bent using a rotary tool. Induction bending is often used to bend large pipes, in applications requiring tight tolerances or sharp curvatures. The heat generated in the process helps reduce residue stresses.

Techniques affecting material thickness
In mechanised manufacture, the desired structure is produced by removing material from the pre-form blank, using various types of equipment. All equipment generally used in steel processing can also be used for stainless steel, but usually at a lower working rate. Turning and milling are the most common methods. Grinding is usually only used on stainless steel in the manufacture of high-precision components and for surface dressing.

Casting techniques
The various casting methods can produce both large, simple structures and structures requiring high precision and good surface quality. Cast structures possess good structural properties and casting can be used to produce sculptured shapes.

Large architectural components are traditionally produced by sand casting. The sand is pressed into the desired mould shape, in a wooden or metal form. The steel is then cast into the mould after the form has been removed. This method can be used to produce structures and components in a wide variety of sizes and shapes. The centrifugal casting method is used to produce hollow, cylindrical structures. In resin mould castings, steel is cast into breakable, resin-bound sand moulds. This method makes possible a higher degree of precision and a finer surface quality than does sand casting, since the sand is finer. Wax mould casting has gained in popularity in recent years. In this method, wax patterns are used to make a wood-like structure, which is then coated with the actual mould material. The wax is then melted off, leaving the casting mould.

4.3 Construction site techniques
Storage
Storing steels requires great care, since the surfaces have to be protected against damage and dirt. Steels must be stored in dry, clean premises. Products must be accompanied by accurate instructions for storing, handling and installation, in order to protect the surface quality.

After delivery, steels must be inspected for any surface defects. Protective materials should not be removed until absolutely necessary. All contact with carbon steels should be avoided and, if required, stainless steels should be protected against any surface contact. Chemicals, oils and greases may also damage or stain the material. A separate, dedicated set of hand tools must be used for processing stainless steels, and any metal brushes and metal files must be made of austenitic stainless steel.

Installation
Stainless steel structures can be fixed using welded joints, bolted joints or other mechanical fixings. In some cases, adhesives can also be used.

Installation procedures for stainless steel products should be set out in writing. They should pay particular attention to the structure’s properties, site conditions, tools and equipment required, trial installation, installation stages and auxiliary structures, lifting points, weight of parts and any temporary supports and braces. In the installation process, the part should not be subjected to harmful deformation or stress.

Welding
Stainless steels are welded using normal welding methods, with applicable equipment and consumables. The welding method is selected on the basis of joint type and thickness, shape and location.

A careful welding plan has to be drawn up for the welding of stainless steel structures. The plan should indicate the correct filler metal, shielding gas and welding flux, applicable voltage and current, travelling speeds, working positions, required preheating and post-weld heat treatment, and the welding sequence.

In welding, special attention must be paid to stainless steel’s thermal expansion properties. While the thermal conductivity of austenitic stainless steel is lower than that of carbon steel, thermal expansion is higher. Asymmetrical thermal movements should be taken into consideration in the welding sequence. Deformation may occur in slim structures, but this can be prevented by preheating.

Welded areas normally require post-weld finishing, for reasons of both corrosion resistance and appearance. Welding affects the properties of stainless steel and makes finishing necessary. Swift installation and optimum final quality can be ensured by using mechanical fixings, not welded joints, on the construction site. From the point of view of the long-term durability of the stainless steel, however, welded joints are recommended over mechanical joints, since a welded joint contains no crevices or other points of discontinuity susceptible to corrosion and staining. For this reason, stainless steel structures should be prefabricated to the maximum degree before arrival at the construction site. This should be taken into consideration at planning stage.

Mechanical joints
When using mechanical joints on stainless steel structures, it should always be borne in mind that the corrosion resistance of the fasteners should be at least equal to that of the joined stainless steel. In bolted joints where corrosive conditions between carbon steel and stainless steel cannot be avoided, the steel grades must be galvanically insulated from each other.
Stainless steel fasteners are used not only in joints between stainless steel structures but also in joints between stainless steel and other materials, and in joints where neither part is made of stainless steel. Typical fasteners made of stainless steel include screws and rivets, bolts and various steel ties and anchors. Self-drilling stainless steel screws are particularly often used in the installation of thin-gauge sheets. Screws and rivets are used in the fixing of light and soft materials, such as aluminium, plastic and wood. Stainless steel bolts are used in the installation of heavier components, such as in the on-site installation of steel structures. Steel ties and steel anchors are usually made of stainless steel, since they are used in applications requiring good long-term durability.

Adhesives
In some cases, stainless steels can be fixed using adhesives, including epoxy, polyurethane, acrylic resins, phenols and resorcinols. The advantages of using glued joints include the possibility of joining different materials, even stress distribution, light weight, the elimination of corrosion between metals, the use of the adhesive as a moisture barrier, good processing properties, and low cost. However, there are many restrictions concerning the pre-treatment of surfaces, the hardening of joints, temperature and fire resistance, toxicity and long-term durability.

Experience to date suggests that the most suitable use of adhesives is in applications such as interior panelling, which involve only minor, unchanging environmental stress and no temperature or humidity problems. Adhesives have also been used in some special industrial applications.

4.4 Applications
Frame structures
Stainless steel’s excellent technical properties make it possible to build economical, lightweight frame structures. In load-bearing structures, stainless steel can be used without fireproofing in fire resistance class R30, which opens up new possibilities for the structural and architectural design of low-rise buildings. With fireproofing, the possibilities are almost unlimited.

Advantages offered by stainless steel include:
- the light weight of structures, without loss of load-bearing capacity
- swift erection
- the reduced space requirement
- the high degree of prefabrication
- the broad range of architectural possibilities

The material properties of stainless steel can be used to particularly good effect in tall buildings. As towns expand and building land becomes scarcer and more expensive, stainless steel is increasingly proving an intelligent choice of frame material. Due to its excellent strength and processing properties, stainless steel is highly suitable for structural use. The initial investment cost may be slightly higher but, in the long term, a stainless steel frame is a competitive alternative to structural steel, both in terms of costs and properties. As our experience of the use of stainless steel increases, planning stages will become shorter and more information will be obtained about stainless steel’s special properties, to serve as a basis for dimensioning norms.

Translucent roofs
Translucent roofs have become more popular in recent years, used both in new buildings and renovation projects. Typical applications include atriums in commercial and office buildings, access passages or building parts designed for the express purpose of admitting light. External spaces are also often covered with translucent structures.

Steel is the most common load-bearing structural material for translucent roofs. As stainless steel requires no surface treatment, it often provides not only the easiest but also the most attractive alternative, and the least expensive. Because loads can be transmitted to the building frame by means of very slender structures, the area of translucent material can be maximised. Furthermore, in the design of steel structures, interesting solutions can be employed to enliven the space. Fasteners and joints are simple and stainless steel does not suffer from weathering problems.

Balconies
Stainless steel balcony structures are now in common use in both new buildings and apartment-building renovation projects. The low weight of the structures and their ease of installation make for an ideal, simple solution in refurbishment projects, and the balconies’ appearance is such that they are suitable for a wide range of façades. Stainless steel surfaces are easy to keep clean, weather resistant and durable, and the balcony structures can readily be combined with glass and aluminium, to produce a light, practical and durable total solution.

Canopies
Canopy structures require only thin-gauge materials and lightweight frame structures. The purpose of canopies and shelters is often not only to protect against the weather, but also to make the environment more pleasant. Being easy to clean, stainless steel is a practical choice for bus shelter structures, for example, as well as other public facilities.

5.5 Bibliography
/1/ ENV 1993-1-4, Eurocode 3: Design of steel structures. Part 1-4: General rules. Supplementary rules for stainless steels. CEN 1996.
/2/ Design Manual for Structural Stainless Steel Second edition, Euro Inox, Luxemburg 2002
/3/ Zulassung Z-30-3-6. Bauteile und Verbindungselemente aus nichtrostenden Stählen. Düsseldorf. Informationsstelle Edelstahl Rostfrei. 1999.
/4/ ANSI/ASCE-8-90. Specification for the design of cold-formed stainless steel structural members. New York. American Society of Civil Engineers. 1991.
/5/ Steel Norm Card no. 6/1997. Use of rectangular hollow sections manufactured by Stala Oy in load bearing structures complying with standard SFS-ENV 1993-1-1. The Finnish Constructional Steelwork Association.

5 Surface structures
5.1 Thin-gauge sheet structures
Dimensioning
The excellent strength and corrosion resistance properties of stainless steels make possible the use of thin-gauge sheets. In roofing applications, for example, this means that the weight of substructures can be reduced. The low material thickness must be taken into consideration when joining the steels with other materials, as must the choice of fixings.

As well as low material thickness, other crucial factors to be considered concerning thin-gauge stainless steel sheet include:
- thermal expansion
- electromagnetic insulation
- surface finish and patterning
- the lack of dressing
- the possible staining of particularly glossy surfaces through handling
- the avoidance of contact with carbon steels

Surface finish and surface treatment method will influence the dimensioning of thin-gauge stainless steel sheet structures. Patterning and reflectivity should be considered when planning joints and sheet layout. The parallelism of the sheets in the finished structure must always be indicated in the plans.

Thermal expansion is an important factor to consider, particularly with regard to joints. If thin-gauge sheets become “butted” due to thermal expansion, they may bend. This would be clearly visible, particularly on glossy surfaces. Fixings also require an allowance for expansion.

Joining
The joining and fixing of thin-gauge steel sheets involves certain special requirements, related to the low material thickness and weight, the tendency to extensive thermal movement and bending, and to water tightness requirements. These factors apply to all thin-gauge sheet structures, but are more pronounced in the case of thin-gauge stainless steel sheets.

Thin-gauge sheets are normally fixed using screwed joints. Welded seams can be used in roofing applications, to produce a tight and neat surface. In dry, indoor applications, adhesives can also be employed. The strength of the steel grade is a determining factor in selecting screws and other fixings. Thin-gauge stainless steel sheets are harder than carbon steel sheets. It is often not possible, therefore, to use self-tapping screws on the sheet without first drilling the sheet and then inserting the screw into the drilled hole.

The most important factor to be borne in mind when fixing thin-gauge sheets is that the corrosion resistance of the fixings should be equal to that of the sheets. In addition, the properties of the material to be joined with the thin-gauge sheet must be considered. The advice of the designer regarding thermal expansion must be taken into account.

Construction site techniques
After finishing, thin-gauge sheets should normally be protected with a plastic cover. The supplier of the plastic material must specify its weather resistance, and the date after installation at which it should be removed. The supplier should also be requested to provide cleaning instructions.

If thin-gauge sheets have to be cut, the blades used must be in good condition, and thoroughly cleaned if previously used to cut carbon steel. Careful cleaning is essential for all surfaces and tools coming into contact with stainless steel that have previously been used to process carbon steel. It is also important to choose the correct side of the sheet for cutting, because of edge bending. If thin-gauge sheet is cut into plates, the direction has to be marked to ensure parallelism of the plates in subsequent processing. This is particularly important for polished and brushed surfaces.

Maintenance and care
Maintenance planning
Post-installation maintenance procedures for stainless steel have to be carefully considered at design stage. Dirty water running down the structures from the roof should be avoided. The usual direction of rainfall, on the other hand, can be exploited in such a way that rainwater rinses the entire surface as uniformly as possible. Grooves, holes and complex patternings that are hard to clean should be avoided. Joints should also be planned to avoid dirt accumulation. Other materials must not release any substances that will stain or otherwise harm the stainless steel surface. The visibility of scratches and other defects can be minimised by choosing a suitable surface finish.

Cleaning
While stainless steels are extremely durable and require very little maintenance, regular cleaning is still necessary, both for outdoor and indoor applications. Stainless steel façade cladding, for example, can be washed at the same time as the windows.

Stainless steel surfaces can be cleaned effortlessly, with just water and detergent. Normal dishwashing detergent, in fact, has proved ideal for the purpose. The surface must not, however, be scratched in the washing process. Structural parts can be cleaned using water, a scrubbing brush and detergent or some other cleaning agent, such as ammonium solution. After the surface has been cleaned, it should be rinsed with clean water and wiped dry. Surfaces have to be inspected at suitable intervals to detect any mechanical defects, signs of corrosion or staining. The special properties of the different surface finishes must be taken into account in cleaning. Brushed steel surfaces, for example, have to be cleaned in the direction of the pattern. Large façade surfaces can be cleaned with a jet washer. If the structures are of coloured or painted steel, special caution must be exercised to prevent damage. Scratches are especially visible on chemically coloured stainless steel, and surface defects are difficult to repair. A painted surface is also easily damaged.

Any exposure of stainless steel to iron or carbon steel can be detected during inspection, and the traces of such exposure can be removed. Iron residues are removed by pickling or passivating, after all other impurities have first been carefully cleaned from the surface.

A stainless steel surface that has been properly cared for, regularly inspected, correctly designed and well built will endure quite severe atmospheric conditions longer than other structures. Where the main specified criteria for a structural part include maximum service life, minimum need for maintenance, or excellent resistance to corrosive atmospheres, stainless steel usually represents the only practical solution amongst currently available materials.

5.2 Façade solutions
Most stainless steel façades are found in public buildings or other building projects that involve significant investment cost. Long-term durability is the most important advantage offered by stainless steel in façade applications. Corrosion from impurities contained in urban air today affects all building materials, to varying degrees. Stainless steel is often also used to convey a modern or sustainable image.

New York’s Chrysler Building, completed in 1930, was the first and one of the most conspicuous projects to use stainless steel as a façade material. When the stainless steel cladding elements and details of the building were cleaned and inspected, they were found to be undamaged, after a service life of 70 years, despite the high corrosion-risk level of the city environment. Stainless steel was used in some external cladding projects in the 1940s and 1950s, particularly in the United States. In fact, for over 50 years, buildings intended to convey an advanced or high-tech outlook, in particular, have been constructed with stainless steel façades. In industrial buildings, stainless steel is most often chosen for the façades in applications where long-term durability is the dominant criterion.

Designing stainless steel façades requires careful assessment of atmospheric corrosion risk, and judicious selection of steel grade. Stainless steel’s wide variety of surface finishes offers the designer broader possibilities regarding the façade appearance than are possible with most other materials. The material thickness of the sheets, the total area of continuous sheets and the way they are joined also influence the reflectivity of the surface. This should particularly be taken into account in the case of large, continuous surfaces.

Thin-gauge stainless steel sheet affords good resistance to mechanical stress. This can be especially useful in roofing, since using light-gauge roofing sheets can reduce the weight of a roof. The roofing sheets can be fixed to the substructure and welded together, which creates a tighter and more uniform surface than can be achieved with other fixing methods.

In modern architecture, large glass surfaces are often combined with stainless steel, since both materials have a long service life. Stainless steel’s remarkable strength properties make it possible to use lightweight structures, and the two materials are highly compatible in terms of appearance. Double glazed façades are a typical application.

5.3 Internal structures
The critical material characteristics for internal applications include resistance to wear, ease of cleaning, visual appearance and light reflectivity. This makes it essential to select the most suitable stainless steel finishing for the application.

In indoor applications, thin-gauge stainless steel sheet is used for decorative surfaces and surfaces subject to wear. Examples of the latter include various flat surfaces and floors. In these cases the most significant material property is mechanical durability. A steel surface is also easy to clean. Scratching may pose a problem for smooth surfaces. On decorative surfaces, it is possible to use ferritic stainless steels, whereas in other construction applications, austenitic steels are used almost exclusively.

Stainless steel components include details, doors, balustrades, dividing walls, mouldings, grips and handles, lighting units, internal staircases and several other architectural interior structures. Many are made almost entirely of stainless steel. Other typical stainless steel applications include water taps and other sanitary fixtures. Often, stainless steel is used in combination with other materials and in large surface applications requiring optimum durability plus easy maintenance and cleaning.

6 Projects
Aspotalo
Office building
Helsinki, 1990
Architect: Eero Eskelinen

Aspotalo, in Helsinki, is one the first buildings in Finland for which a higher alloyed stainless steel is extensively as the main material for the façade architecture. The building, located in the Herttoniemi area of Helsinki, was completed in early 1990.

Aspotalo’s main façade materials include stainless steel and white ceramic tile. The building parts and walls below the main entrance, at ground level, are granite. The tall, stone wall is complemented by adjacent lightweight steel masses. A fixed, steel sunscreen structure enlivens the wavy south-western façade. The slanted roof surface that extends the cassette façade on the side of the building is also stainless steel, while the third material used in the building is glass. Steel façades have continuous windows, while windows in the stone surfaces are individual openings. A steel and glass tower serves as a landmark, guiding people to the entrance of the building. Choice of materials was based on the nature of both the physical and cultural environment and on the metals associated with the business of the building’s original owner. Because of the marine atmosphere and the proximity of the oil harbour, steel used on the external structures is acid resistant.

All external steel parts of the building – including the façades, the roof, the steel straps and L-beams of the clinker façade, the owners’ logos, railings, door frames and flagpoles – are in molybdenum-alloyed steel, grade 1.4401.

Cassette façade system
The stainless steel cassette façade consists of two levels.


The cassettes and continuous windows form the basic surface – the background. The visual structure above the surface of the street-side façades consists of horizontal tubes and pipe systems above the windows. These pipe systems do not appear on façades furnished with sunscreens. On straight, sheltered façades the cassettes are installed horizontally, the horizontal seams masked by the tubes. On the wavy façade they are positioned vertically. These vertical cassettes are edged, so the cassette can be curved into a cylindrical surface. The cassettes are fixed to stainless steel vertical purlins with concealed fixings. Visible seams are mostly butt joints.

Sunscreens
The sunscreens form an independent system, outside the façade, with the balustrade on the top-floor terrace a homogenous part of the system. Sunscreens and balustrade form a kind of a flexible fabric in front of the façade, suspended by vertical tubes from terrace-level edge beams. The cassette façade is penetrated by “knives,” fixed to the concrete at fairly wide intervals. The vertical tubes are supported on these knives by loose sleeves and flexible bolted joints. The knives transmit lateral forces, and a welded structure, consisting of horizontal tubes, inclined consoles and grating frames, is installed between the vertical tubes, fixed with collar/sleeve joints. The actual sunscreen – an inclined, acid-resistant steel grating – is fixed with screws. The terrace balustrade is fixed to this entity with sleeves and screws, with some play in each system joint. Thermal movement is evenly spread over the entire fabric.

Stainless steel, light and movement
Aspotalo’s stainless steel façade is rich in visual interest. Factors such as the numerous steel details of the wavy façade, the liveliness of the surface finishes and the transparent, net-like appearance of the gratings give it a kinetic quality, full of light and shade. The building reacts to changes in its surroundings, such as the movement of people, passing clouds (reflected by the surface) and the changing seasons, and its appearance and colour alter in different weather conditions.

Architectural design:
Arkkitehtitoimisto Jan Söderlund & Co. Oy (now Sarc Oy)
Eero Eskelinen, Jan Söderlund, architects SAFA
Structural engineers:
Insinööritoimisto K. Hanson & Co.


Office-building extension,
Tornio, Finland, 1996
Architect: Eero Eskelinen

Planning work on the extension and renovation of the façade of this late 1960s steel-mill head office began in the summer of 1992. The spacious industrial plan allowed considerable freedom in determining the extent of additional building and the division of mass. In fact, the surrounding roads act as natural limits to the building area. The new, narrow-framed extension, a little over 1,000 m2 in size and three storeys high, is connected in a 90° angle to the existing two-storey office building, which is almost 100 metres long. This right-angle layout allows for two more extension units, of similar size, to be added later.

A spacious, two-storey lobby connects the old and the new building, with a rather narrow, bridge-like access ramp between the buildings, at first-floor level. A panoramic lift in the extension section opens into this entrance lobby. On the stepped, eastern side of the building, room division is more or less fixed, whereas the size of the office rooms on the western side can be altered.

The central mass, rising above the second floor, acts as a visual core for the building mass, its eastern side opening up to the second floor’s central passage through a continuous upper window. The floodlight mast, which illuminates the external areas, is connected to the building and forms a part of its architecture. The extension is located on the south side of the old office building, and partly over it beside the main entrance on the north side. This entrance has been made prominent, with a new protruding vestibule and a canopy on the north side, which also tie the architectural features of the old and new parts together, using the architecture, materials and details of the new building.

The new building’s main façade material is grade 1.4401 stainless steel.

The tall, central mass of the new section is covered with composite panels, in which two thin-gauge stainless steel sheets are joined using an intermediate stiffening material. The external surface is 0.8 mm, grade 1.4401 steel, with a ground surface finish and embossed, repeating patterning.

Cladding on the outer façade surfaces consists of 150-mm high, 1.0-mm thick profiled stainless steel panels, with a ground surface finish.

On the south-east side of the building, the windows are protected with suspended, inclined sunscreen gratings, made of stainless steel. On the western side, the sunscreens are grating walls, just over 12 metres high, with foundations in the ground. The spacing and mesh of the grating walls follow the basic room module.

The lattice-construction floodlight mast, at the south end of the building, is covered with perforated stainless steel sheets. Rows of lighting units are mounted vertically down the inside corners of the tower, giving it the appearance, at night, of a vertical light beam.

The sand-lime brick façade of the old head office was covered with smooth, thin, light-grey plaster. All windows were renewed, and external metal structures replaced by stainless structures. Grade 1.4401 sunscreen gratings, suspended from posts, were installed on the southern façade, because of heating problems caused by the exceptionally tall windows of the old office building. This also links the architecture of the new building to that of the old in a natural way.

The new building has a steel frame, and hollow-core concrete floor slabs. Its vertical columns – circular stainless tubes, with a ground finish – serve as static load-bearing structures, in themselves. Due to fire safety regulations, however, they have been filled with concrete.

Architectural design:
Arkkitehtitoimisto Jan Söderlund & Co. Oy (now Sarc Oy)
Eero Eskelinen, architect SAFA
Structural engineers:
Insinööritoimisto Erkki Huhta Ky

Laboratory office building
Tornio, Finland, 1997
Architects:
Heli and Tuomo Juola

This office building, located in a steel-works industrial estate, is an annex, built on a north-south axis, connected to a metallurgical laboratory. Factors considered in planning the new building included economic flexibility, a steel structural frame, lightweight façades and the possibility of eventually extending the building.

Grade 1.4401 stainless steel is used in the entrance-lobby columns and the frames of the external glazed roofing. The main-entrance façades and the staircase-balcony tower at the south end are stainless steel and glass. The cladding material of solid parts is steel net panel, mounted 100 mm off the wall surface to conceal the connection point between the new building and the old concrete stair tower. External wall elements are steel and mineral wool. Wall and roofing cladding is a combination of acid-resistant steel profiles and thin-gauge steel sheet panels.

Architectural design:
Arkkitehtitoimisto J & J Ky
Structural engineers:
Insinööritoimisto Pöysälä & Sandberg Oy

Office complex
Finland, Espoo, 1990s
Architect: Eero Miikkulainen

This site is located in an industrial estate off the Länsiväylä arterial road, near the urban district of Niittykumpu. The first building in the approximately 8-hectare area was the precision-mechanics and electronics research laboratory, completed in 1966. This building was demolished in the mid-1990s, but for its load-bearing frame, and an office building erected in its place.

During the following 30 years, development of the estate continued at an even pace. Eventually, five building complexes were completed, to meet the research, production and office-space needs of the company’s various units.

A perforated steel sheet fence, complemented by impressive, post-mounted lighting units, encloses the street side of the area. The entrance has been expanded into a segmented square and furnished with a rather large steel canopy. Supplementary structures include a security gatehouse.

Renovation projects
Renovation activities have mainly involved the interior spaces of three buildings. A more thorough refurbishment has been carried out on the façade of the four-storey office building, which had continuous windows. The smooth-face surfaces of the façades have been covered partly with brick-faced panels, partly with perforated stainless steel sunscreen panels and blades.

Individual canopies, each supported on its own steel structure, give emphasis to the three separate entrances to the office building. The load-bearing structures are profiled structural hollow sections and diagonal braces of EN 1.4301 stainless steel, and the sunscreen panels are 1-mm thick stainless steel sheet, grade EN 1.4401.

New building projects
In addition to work on the annex built onto the head-office building, new building activities were mainly carried out in the vicinity of the entrance area. The gatehouse serves as security centre and mail distribution centre for the area, and as an information office. The structural solutions and materials of the gatehouse follow a line that blends with the overall appearance of the streets and the square. Steel has been used to construct the load-bearing part and the “landmark” tower, and external cladding consists mainly of edged façade cassettes in grade 1.4401 stainless. The roofing of both the actual building and the canopies are molybdenum containing steel sheet. The glass wall on the southern security station of the building is protected by an external sunscreen, consisting of tinted glass blades.

The canopy over the entrance to the area consists of eight elements, suspended from four columns. An internal, cast-concrete layer increases the weight of these elements, to ensure the structure’s stability. Steel structures inside the jackets of the composite columns improve their load-bearing capacity. The columns’ foundations rest on reinforced concrete footings, cast onto steel piles. Completely prefabricated, the columns, complete with the canopy elements and suspension structures, were already filled with concrete when mounted on-site.

Grade 1.4401 stainless steel is used for the column jackets, their secondary and suspension structures and the structural hollow sections on the edges of the plane elements, with a ground finish on visible surfaces. The same steel grade is used for the cassettes on the underside of the plane elements, made of 2.5-mm glass-bead blasted sheet, and the roofing, made of 0.5-mm thick steel sheet with a pickled surface finish.

Architectural design:
Arkkitehtitoimisto
Arkkitrans Oy
Structural engineers:
Insinööritoimisto Pöysälä & Sandberg Oy

Nokia head office
Keilalahti, Espoo
Finland, 1996
Architect: Pekka Helin

This office building is located at a junction of the Länsiväylä arterial road and Ring Road I, some 8 km from the centre of Helsinki and 2 km from Tapiola. Most of the building is surrounded by sea. Its considerable overall volume has been organised and proportioned on a human scale, and the building’s lightness, airiness and carefully considered details, together with the effective space solution, make for a modern and original working environment.

Space solution
The facilities reserved for offices and product development can be altered by dividing rooms on a combi-office, individual office or open-plan office basis. The working and service facilities wind round two large atriums. Common service facilities, located on the ground floor, include a restaurant, a cafeteria, conference and meeting rooms, an auditorium, exhibition space, a gym, dressing rooms and washrooms.

Steel structures
In addition to their practical function, the visible steel structures considerably affect the building’s architectural appearance. The double façade (the first of its kind in Finland) is supported on a frame structure consisting of grade 1.4401 stainless steel profiles. This frame structure, fixed to the concrete façade and suspended from the canopy structures on the roof, also supports the aluminium maintenance grilles on each floor. The additional glass surface and the auxiliary structures of the double façade reduce the consumption of cooling and heating energy. While performing an ecological function, they also serve as an architectural element.

Owner:
Nokia Oyj
Architectural design:
Arkkitehtitoimisto
Helin & Siitonen Oy
Structural engineers:
Insinööritoimisto
Oy Matti Ollila & Co.

Sanomatalo publishing house building
Helsinki, 1999
Architects: Antti-Matti Siikala, Professor Jan Söderlund

In 1995, Sanoma Osakeyhtiö held a restricted competition for the design of a new building for its newspaper-publishing house, located in Helsinki’s Töölönlahti business area, near Parliament House and the station. The 9-storey building houses the editorial offices of Helsingin Sanomat, Ilta-Sanomat and Talous-Sanomat, while the ground floor and first floor are reserved for shops, galleries and restaurant facilities, accessible from pedestrian passages. All in all, the building serves as workplace for some 1,000 people.

The base plan of the Sanomatalo building is a square, diagonally divided by two public, pedestrian passages. The space between the passages, on the northern side of the building, is designed as a full-height town space, the Media Market, looking out on Töölönlahti through a 35-metre high glass wall.

The building’s open character is emphasised by extensive use of glass on external façades. Indeed, the sections containing office facilities are designed with double façades. A second façade, consisting of single-glass panes, is mounted 90 cm from the actual glass façade, as a weather-protection measure. This solution facilitates control of indoor air quality. External façade structures are made of glass-bead blasted stainless steel, grade 1.4401, selected mainly for its low need of maintenance. Brown, oxidised, corrugated copper and plain copper sheeting are used on surface cladding.

The glass units forming the inside walls of the double glass façades are 2.7 metres wide and the height of the space between the floors. They have factory-prefabricated steel frames. The outermost panes are supported from the edge of the intermediate floor slab on each floor by means of stainless steel structures. This outermost glass wall continues as a cantilevered wall at the corners of the building, and on the roof terrace. Welded profiles are used for the steel frame of the inside façade elements and for the stainless support structures of the outermost panes.

Gross area 43,000 m2
Volume 231,000 m3

Owner and Project
Management:
Sanoma Osakeyhtiö
Architectural design:
Arkkitehtitoimisto Sarc Oy
Antti-Matti Siikala, Professor Jan Söderlund. Architects: SAFA
Structural engineers:
Insinööritoimisto Magnus Malmberg Oy

Stockmann department store extension
Helsinki, 1989
Architects: Kristian Gullichsen, Erkki Kairamo, Timo Vormala, Jaakko Sutela

The Stockmann department store extension, in the centre of Helsinki, was completed in spring 1989. The department store itself, designed by Sigurd Frosterus, was built in 1930. Neighbouring buildings include a decorative castle in French Renaissance Revival style, designed by John Settergren and built in 1889, the property on the opposite side of the street at 1 Keskuskatu (a street), designed by Eliel Saarinen in 1920, and two buildings designed by Alvar Aalto, from 1955 and 1969. At one end of Keskuskatu, the last building is Eliel Saarinen’s railway station, completed in 1918. The last building at the other end is the Swedish Theatre, the new façade of which was designed by Eero Saarinen in 1936.

Over the years, numerous plans were prepared for an extension of the department store. Frosterus drew up several, between 1924 and 1956 and Aalto presented two alternatives in 1961 and 1966. All these plans would have involved demolishing Settergren’s neo-Renaissance building.

The triad (Frosterus/Settergren/extension) that finally resulted illustrates the history of Finnish architecture, with an average of some 50 years separating each of the three examples. Each building represents its particular era. The earliest demonstrates the eclecticism of the late 19th century. The latest illustrates the translucent architecture of light, the concern for context and the ambiguity of meaning favoured in the modern architectural tradition (Arkkitehti Magazine 5-6/89).

The Stockmann department store extension project was carried out on the basis of the winning entry in an architectural competition. In the solution, John Settergren’s 19th century, Renaissance Revival façade has been preserved in the façades of the building that face the Mannerheimintie Road and the Pohjoisesplanadi Road. The new façade is made of granite, glass and stainless steel.

The extension’s interior is very light and airy, its mainly light and neutral colours being particularly suited to the frequent changes of display typical of a department store environment. Stainless steel has also been used in internal structures such as the lift structures and the balustrades that mould the space. The way in which stainless steel is used enhances the building’s airy feel.

Architectural design:
Gullichsen, Kairamo, Vormala, architects
Structural engineers:
Juva Oy

National Library of France
Paris, 1995
Architect: Dominique Perrault

The library is located in the south-eastern part of Paris, on the left bank of the River Seine, in the 13th arrondissement. Dominique Perrault’s competition project consists of a rectangular public square with an open-book-shaped tower building at each corner, research and exhibition facilities, reading rooms below the level of the square, an atrium with planted trees, and a wooden staircase leading from the street to the square. The idea behind the design was to develop the former wasteland area and create a reputed city landmark and public square.

The library has a collection of some 12 million books, the earliest dating back to the invention of printing, all located on the eleven upper floors of the tower buildings. Administrative facilities take up the seven lower floors, while the two top floors are reserved for technical facilities. The researchers’ facilities are located at atrium level, and the 13-metre high reading rooms, seating about 3,500 people, are above the researchers’ facilities. The main entrance to the library is at the reading room level.

The library’s external shell is constructed using three materials. One is stainless steel, used in a variety of ways, including matt finish plates and woven grilles. The building mass also incorporates trees and bushes, surrounded by stainless steel frames.

Woven stainless steel panels and nets are used both for the external and internal spaces. Inside, they serve as sound insulating surfaces on walls and ceilings. Perrault has also used woven stainless steel nets in other projects – for example in the external cladding of the velodrome and swimming stadium in Berlin.

Architectural design:
Perrault architecte
Perrault Associés SA
Perrault Projets SA
Structural engineers:
Ove Arup & Partners

Helsinki-Vantaa Airport
1st and 2nd phase of Central Terminal
International Terminal T2
1996-1999
Architect: Professor Pekka Salminen

The international terminal at Helsinki-Vantaa Airport was expanded in two phases. The first expansion phase of the so-called Central Terminal, completed in the autumn of 1996, consisted of passenger lounges, six new passenger-boarding bridges, two bus gates and commercial service facilities.

The second Central Terminal construction phase, completed at the end of 1999, included a terminal to handle an annual traffic of six million passengers, with departure and arrival lounges (a baggage reclaim hall and an arrivals meeting-point area). This second phase also involved changes to ground traffic arrangements, including providing pedestrian passageway access to the domestic terminal.

Internal spaces
Materials and colours were selected with the intention of creating a calm, discreet general effect, complemented by carefully planned details. The main materials include steel (painted a metallic colour) and aluminium, granite on the floors, steel-grey laminate surfaces on internal walls, and plenty of glass. Those building parts subject to wear are made of stainless steel. On some wall surfaces and details, maple and teak elements have been incorporated, to counterbalance the steel.

Steel in entrance structures
The most demanding steel structures of the second phase were the departure lounge entrance canopy (with its glass and steel structures) the ventilation tower and the lattice framework. These steel lattices are supported on diagonal struts, stiffened with stainless steel tension rods, and the roof sections between the lattices are supported by stainless steel truss frames. The structure is further complicated by the thermal break between the cold roof structure and the translucent roof of the heated space. In order to prevent asymmetrical structural loading, both the glass translucent roof and the glass canopy are equipped with electrical heating. Roof glazing is fixed using the so-called semi-SG system and façade glazing using point fixing.

Sunscreen structure on the access passage
A sunscreen structure in front of the façade screens the continuous windows of the access passage, while also serving as a mount for the tracks of the window maintenance cradle. The sunscreen is constructed using perforated stainless steel cassettes, attached as flag-like elements to steel frames fixed to the façade. These steel frames are stiffened with compression members and tension rods. This sunscreen structure provides visual uniformity to the building when seen from the access road, and makes the scale of the access passage comprehensible. The web-like nature of the steel structure and the semi-translucent perforation of the cassettes create a three-dimensional visual effect.

One clear advantage of using steel in the construction was that much difficult and time-consuming work could be carried out at engineering plants rather than on-site. This made it possible to keep within the tight building schedule.

1st phase:
Gross area 16,489 m2
Volume 77,850 m3
Conversion of
existing facilities 14,498 m2
2nd phase:
Gross area 30,883 m2
Volume 155,400 m3
Conversion work
included in gross area
Total of 1st and 2nd phases:
Gross area 47,372 m2
Volume 233,250 m3

Owner:
CAA Finland
End-user:
Helsinki-Vantaa Airport
Architectural design:
Arkkitehtitoimisto Pekka Salminen Oy
Structural engineers:
Insinööritoimisto Pöysälä & Sandberg Oy

University of Tampere
Construction Phase III
Tampere, Finland, 1993
Architect: Antti Katajamäki

This building, located on the western side of the campus area, contains the facilities of the Economics and Administrative Science departments, accommodating a total of some 2,800 students and 200 staff. The building mass divides into three parts: a cubic gate section, a curvilinear department section, and a bridge-like access section connecting the other two sections.

Construction Phase III of the University of Tampere is the first public building project in Finland fully conceived in steel.

The building frame consists of steel columns and beams, while the floor construction is mainly a composite slab structure, with hollow-core slab used for the side parts of the gate section. A steel suspended bridge construction supports the access section.

The gate section’s façade cassettes are stainless steel and the departmental section’s cassettes white PVF2 coated steel plate. Stainless steel is also used in the visible cladding of the ventilation ducts in the gate section lobby.
The architecture successfully gives the impression, albeit discreetly, that this is a major public building. Construction Phase III does not attempt to be a continuation of the main building, completed in the 1960s, but is, rather, an independent building, employing the methods and materials of its time. In this respect, it brings out the mix of periods represented on the campus.

The façades reflect the activities carried out behind them. The department section’s repetitive window spacing and the hierarchical network of seams on the metal cassettes follow the rhythm of the chain of individual rooms behind the external walls. This concept takes its inspiration from information technology – the basis of the building’s function. The “leading edge technology” metaphor reaches its apex at the northern end of the building, where the mass curves up into a sharp peak, covered with high-gloss stainless steel sheet. The gate section’s distinctive appearance, reflecting the nature of the common public facilities inside, is based on compactness of volume, neutral façade division and the use of ground stainless steel as a cladding material.

The same material and shapes repeat in both the external and internal architecture. Stainless steel, either with a smooth or a perforated surface, covers the building’s envelope, protecting the windows, borders and access bridges and giving a final touch to the fixtures. The numerous, clear design goals and details make the building a harmonious and stimulating environment in which to study.

Gross area 9,436 m2
Floor area 8,747 m2
Volume 34,150 m3

Owner:
National Board of Public
Building
Tampere University Foundation
Architectural design:
Arkkitehti- ja rakennuttaja-toimisto Antti Katajamäki Ky
Structural engineers:
Insinööritoimisto TE-EM Oy

Bergianska trädgården
Botanic Gardens
Stockholm, 1994
Architect: Per-Rune Semrén

In 1936, Edvard Andersson, a Swedish wholesale businessman, bequeathed one million Swedish crowns to the Bergianska Foundation, to fund the building of a greenhouse. This winter garden was to be designed specifically for growing Mediterranean plants, trees, bushes, flowers and herbs. The Royal Swedish Academy of Sciences, in charge of the administration of the Foundation, had the greenhouse built in the 1990s. It was completed in 1994.

The building consists of a main greenhouse, which serves as the actual display space, and standard greenhouses, in which plants are grown before being transferred to the display space.

The main greenhouse is square in shape, its façades extending up to an inclined roof, on which sits a lantern-like structure. In each corner of the main greenhouse, there is a low, square annex. A tall glass hall on the southern side of the central building serves as an access passage to the other greenhouses.

Steel and glass structure
The load-bearing structure of the main greenhouse consists of acid-resistant structural hollow sections, with diameters of 108-355.6 mm and a wall thickness of 8-31.75 mm. Complex joints between hollow sections of varying thickness were designed using a 3-D CAD simulation model. To avoid material waste, a special welded joint was developed for the project.

Structural beams of polished circular section are supported on the main bearer. Screwed joints were developed for various junction angles, to avoid using welded joints between the bearer beams and the substructure. With the exception of the façade corners, there are no right angles in the building. Overall, the structure incorporates a wide variety of individual solutions.

Separate fixings, mounted on the bearer beams, form a straight substructure for the glazed roofing. The intermediate elements between the

steel structure and the glazed roofing, manufactured specially for the project, accentuate the impression that the glass is floating above the frame.The roof has an insulating glass structure, with 10 mm glass on the outside, a 16 mm intermediate space, and 6 + 6 mm glass on the inside. Glazing is mostly in bright glass. At some points, individual patterned glass panes are used as sunscreens. The insulated glazing material of the standard greenhouses is polycarbonate.

Construction phase
1992-1994

Total area 3,200 m2
Main building area 2,000 m2
Area of standard
greenhouses 1,200 m2
Total glazed area 3,350 m2
Roof glazing area 2,000 m2

Owner:
Royal Swedish Academy of Sciences
Architectural design:
Semrén & Mansson, Architects
Structural engineers:
Arne Johnson, Engineering Office

University of Helsinki
Biocentre 1 A
Helsinki, Viikki, 1996
Architect: Kaarina Löfström

Located in the University’s Viikki campus area, in the Helsinki Science Park, this building is mainly used by the Applied Chemistry and Microbiology department, the Bio Sciences department and the Institute of Biotechnology.

The “sliced” form of the building volumes reflect the other university buildings in the area, designed by architect Veli Paatela in the 1960s. Individual slices house different functions, such as reading rooms, auxiliary facilities and laboratories. The curved building volume on Viikinkaari (a street) contains common facilities, such as teaching laboratories and administrative premises. The canteen and the library are located in separate spaces, at each end of the building.

In terms of scale, the objective was to integrate the building into the environment of the Latokartano district by stepping the mass on the Viikinkaari side. The laboratory slices on the opposite side are also stepped. The main entrance is highlighted by the canteen’s two-storey steel-and-glass wall, which serves as a background for green plants.

On the façades, burned, light-coloured, cast-in-place brick alternates as a cladding material with dark, corrugated, thin-gauge, metallic-finish sheet metal and stainless steel sheets. The stainless steel composite cassette uses thin material gauges, the external plate being 0.7-mm thick grade 1.4401, 2B finish, and the internal plate on the inside of the 15-mm thick intermediate material being 0.6-mm thick sheet; which produces an non-reflective surface. The fixing clips are polished. Part of the façade cladding, such as that on the inclined walls of the recreational facilities and the library, is made of diamond-patterned sheet. These walls are constructed in a similar fashion to the straight walls.

Gross area 16,000 m2
Floor area 14,000 m2
Volume 61,000 m3

Owner:
Real Estate Company
Biokeskus 1 A
Architectural design:
Arkkitehtitoimisto
Kaarina Löfström Oy
Structural engineers:
PI-yhtiöt Oy

Institute of Information Technologies
Helsinki University of Technology
Otaniemi, Espoo
Finland, 1998
Architect: Juhani Maunula

One of the factors that made the design work for this building quite challenging was its location, opposite the main building of the University of Technology (designed by Alvar Aalto). An absolute requirement was that the main cladding material should be red brick, to link the building with existing building stock in Otaniemi. On the other hand, the designers wanted to complement the brick with steel, a modern building material, both to reflect the Institute’s future-oriented activities and to lighten up the overall appearance.

The building was designed to be as flexible as possible, to allow modifications at a later date. Security also played an important part in the design. For functional and security reasons, the building plan is based on a central-lobby model, in which the teaching and working spaces surround a top-lit courtyard, constructed in steel, containing the pulsating heart of the building, including the cafeteria/restaurant and the library. The galleries above these facilities are used as student teamwork rooms.

Since Information Technology is developing faster than any other field, the designers sought to give the Institute’s central building a strong personal identity. This is exemplified in, for example, the auditorium cubes (clad in stainless steel) that overhang the entrance courtyard.

On the façades, steel appears in a wide variety of forms: as stainless steel cladding, powder-coated steel sheet, elements with steel covering, steel net, squared grilles, steel columns, frame structures, tension rods, etc. Stainless steel has also been used as an internal cladding material on large, impressive surfaces.

Gross area 13,000 m2
Useful area 8,000 m2
Volume 62,000 m3

Owner:
State Real Property Agency
End-user:
Helsinki University of Technology
Institute of Information Technologies
Architectural design:
Arkkitehtitoimisto Brunow & Maunula
Structural engineers:
Finnmap Consulting Oy

Helsinki Vantaa Airport car park, 1994
Architect: Professor Pekka Salminen

This circular, 200-car parking facility, in front of the domestic terminal, is largely underground. It consists of seven circular parking levels, four of which have been excavated in rock. Viewed from the airport’s access road, the lightly curved steel surface appears to be that of a building of only two storeys.

The façade cladding material is ground stainless steel sheet. Each cassette, made of 2-mm thick perforated sheet, is fixed to the tubular frame supporting the façade by four stainless steel bolt fixings and cap nuts. The use of perforated sheet provides the requisite openness and fire ventilation for the levels located above ground.

It was the end-user’s wish that the colour of the façade be as light as possible. In the original plans, the material was to be glass-bead blasted matt-finish steel, but this was later replaced by a ground finish. The lightness of this surface depends on the direction of the grinding, as well as on how sunlight falls on it and how the observer is positioned in relation to the perforated sheet surface. Optimal cassette rigidity was obtained by aligning the perforations in straight rows.

Other applications of stainless steel in this project include the plastic-coated steel cassette surface on the stairwell façade, which is horizontally divided by stainless steel mouldings, 50 mm high. The staircase balustrade is also made of perforated stainless steel sheet. Painted steel is used for the taxi shelter structures, while their tension rods, gutters and eaves flashing are ground stainless steel.

The walls in the access tunnel between the domestic terminal and the car park are covered with the same stainless steel cassettes as the façades. Concealed behind these cassettes are the ventilation and electrical installations.

Gross area 56,070 m2
Volume 139,450 m3
Parking spaces 2,024

Owner:
CAA Finland
Architectural design:
Arkkitehtitoimisto Pekka Salminen Oy
Structural engineers:
Insinööritoimisto Oy Eero
Paloheimo & Matti Ollila

Ruohoparkki Car Park, Helsinki, 1999
Architect: VP Tuominen

At the end of 1994, an architectural design competition for the building of a multi-storey car park, in Helsinki’s Ruoholahti district, was arranged.

The competition proved challenging, since the car park was to be exceptionally large, by Finnish standards, requiring 10-11 storeys. Its situation, at the end of the western radial road leading to Helsinki, in the new-town section of Ruoholahti, later to be filled with office blocks not yet planned or built at that time, put considerable demands on the building’s architecture, façade materials and preliminary layout.

The building uses thin-gauge stainless steel sheet and thin-plastered, ground and painted concrete in the façade structures. The objective of this solution was to create a unified but detailed whole, that would support the surrounding townscape. Thanks to the properties of the chosen façade materials, the architectural approach could be simple, and yet incorporate all the functional, economical and technical characteristics required.

The steel façade parts are made of stainless steel sheet, 1.25 mm thick, perforated and profiled as a stiff structure. Profiled sections are fixed on the raised, horizontal, stainless steel strips of the intermediate floors. Perforated sections act as windows and afford supplementary ventilation. Stainless steel is a low-maintenance material, highly suitable for façades subject to the effects of urban surroundings and a marine atmosphere.

Floor area 25,300 m2
Volume 74,000 m3
Parking spaces 790

Owner:
Ruohoparkki Oy (owned by the companies based in the adjoining offices: Nokia Oyj, YIT-Yhtymä Oy, Oy Metra Ab)
Architectural design:
Arkkitehtitoimisto VP Tuominen Ky
Structural engineers:
Insinööritoimisto Magnus Malmberg Oy

Helsinki Metro
New sanitary-facilities concept
1990s
Architect: Esko Miettinen

At the planning stage of the Helsinki Metro (underground system), the stations’ public sanitary facilities were designed as rather large, separate units for men and women. Difficulties were eventually encountered in managing these oversized facilities, which could consist of up to 10 men’s and 15 women’s cubicles, plus an entrance area. As a result, some of the units had to be closed. The architect and the Helsinki City Transport Building Office, developed a new solution based on automatic public toilets (APTs). These new toilet units are accessed directly from the busy Metro passages. There are two such toilet units and one urinal unit in every station. Toilets combining facilities for handicapped passengers and infant care were also designed. Stainless steel, already widely used in the Metro in numerous applications, was selected for the units’ external façade and internal walls.

Owner:
Helsinki City Transport
Architectural design:
Esko Miettinen, SAFA architect

Standard Helsinki kiosk structure
1994-
Architect: Jaakob Solla

In late 1994, the City of Helsinki, the Finnish Association of Architects and the union of fast-food kiosk owners in Helsinki arranged an open competition for the design of a standard kiosk structure. The objective was to find a compact, high-quality, easily modified kiosk structure that could be built at reasonable cost. It had to be suitable as a fast food, ice cream, flower or newspaper kiosk. The winning “Jaffa,” kiosk concept was designed by Tommi Grönlund, Turo Halme, Iiro Mikkola, Petteri Nisunen and Jaakob Solla. A prototype ice cream kiosk was introduced in Itäkeskus in summer 1997, and a fast food kiosk in Malmintori at the beginning of 1998.

There are some 60 fast food kiosks, 40 ice cream kiosks and 20 flower, confectionery and newspaper kiosks in Helsinki. They will all eventually be replaced by the new kiosk structure. Some old kiosks of great historical value, such as that in Esplanadi Park, represent the different eras of Helsinki kiosk design, and will be preserved. Certain special locations will have a kiosk specifically designed for that location.

The external appearance of the kiosk is that of two overlapping cubes, one a steel section containing technical equipment and toilet facilities, and the other an open, glazed, customer service section. The solid section is clad in ground stainless steel sheet, mounted horizontally, and the frame structure of the glazed section consists of ground L- and T-profiles. Stainless steel was selected as the wall material of the solid section for its dimensional accuracy and ease of maintenance. Fixtures inside the kiosk are mainly in stainless steel.

Owner:
City of Helsinki
Estates Department
Architectural design:
Arkkitehtitoimisto a.men Oy
Structural engineers:
Insinööritoimisto Oy Matti Ollila & Co.

Ninety-five apartments
Semape, Paris
1996
Architect: Francis Soler

This apartment building is part of a residential block located on the left bank of the River Seine, in the 13th arrondissement (district), next door to the new National Library of France. The building has a reinforced concrete frame and the façades, mainly glazed, are based on a sliding glazing system. Some apartments are floor-through, but most have windows on only one side. French balconies increase the residential area, and make it possible to convert internal space into external space by sliding the apartment’s entire façade-side glass wall to the side.

The façade-side glass walls of the building contain printed fragments of fresco paintings by Jules Romain, in the form of montages designed by Roman Cieslewicz. The balustrades of the building-length French balconies are slender stainless steel structures, through which the external space can be clearly discerned. Their lightness complements the proportions of the façade and allows the fresco montages to be seen.

Architectural design:
Francis Soler, architect

Into House
Espoo, Finland
1998
Architect: Professor Jyrki Tasa

Built on a high hill, the house has a view to the sea. This 187-m2 house, designed to accommodate a single person, emphasises the role of reception rooms and recreational facilities, and has relatively small bedrooms and service spaces.

The house’s frame is steel, with wooden purlins and girders. Vertical steel structures are 80 x 80 x 5 or circular 88.9 x 4.5 tubes, and horizontal structures either IPE- or U-beams. Circular stainless steel columns and HE 140 A-girders support the terrace’s wooden roof beams, while the bottom floor and the chimney tower are of reinforced concrete. This tower and the curved external wall stiffen the house horizontally. The cladding of the external walls consists of vertical, white-painted boarding, strong, profiled battening and pine plywood. The roofing is machine-seamed flat-sheet metal.

In the courtyard, bright plastic sheeting covers the steel frames of the firewood sheds. The cladding of the internal walls is mainly pine plywood. Floors and visible wooden parts of kitchen fixtures are of cherry. In the fireplace tower, soapstone has been combined with a dark-silver, perforated steel-plate wall.

Total area: 187 m2

Architectural design:
Professor Jyrki Tasa, SAFA architect
Structural engineer:
Pertti Ranta, MSc.

Villa Inox
family house
Tuusula Housing Fair 2000, Finland
Architect: Esko Miettinen

The central theme of Villa Inox is space – for example, the relationship between internal and external space. The semi-open plan includes spaces designed for family get-togethers and private spaces for each family member. Moving outdoors from the inside has been made as easy as possible. Each room has its own outdoor extension space – on the ground floor, part of the courtyard and, on the upper floor, a balcony. The presence of surrounding nature enters the house through, for example, the floor-level windows in the living room and vestibule.

Structure
The main mass of the house is built on a column frame. The columns are almost completely visible in the tall, two-storey living room. Made of stainless steel, the load-bearing frames support the intermediate floor of the two-storey main mass. In the single-storey part of the house, the walls are load-bearing.

External walls are of Termo purlin construction, and the load-bearing frame is a heated structure. Partition walls have steel frames. Stainless steel, as a cold structure, has been used for the load-bearing frame of the car shelter. The Termo purlin element structure is covered with half-lap boarding fixed on battens. The building frame and the wall elements mounted on the frame were prefabricated.

Thanks to the frame structure and the element-based construction method, building time was a mere three months.

Materials
Stainless steel has been used for the load-bearing column frames. In internal spaces, the steel mainly has a ground surface finish, while pickled steel is used in the garage. The main-entrance vestibule, balconies and staircase are also of stainless steel.

The internal cladding of the element walls is painted gypsum board. Flooring is beech parquet and ceramic tile. At the request of the lady of the house, worktops in the kitchen and laundry room are mainly stainless steel. Details such as the identical pull handles and skirting structures, all made of stainless steel, emphasise the uniform effect of the internal spaces.

The roofing and window-sills are made of copper. Downpipes, fence posts and the frames of the external staircases are stainless steel, as is part of the external cladding.

Four rooms, kitchen, laundry room, sauna section, car shelter, storeroom and technical space.

Gross area 178 m2
Net apartment area 159 m2
Plot area 722 m2

Architectural design:
Esko Miettinen, architect SAFA
Structural engineer:
Eero Kotkas, engineer,
Insinööritoimisto Oy Matti Ollila & Co

Bibliography for chapters 2, 3 and 6
A Decade of Architectural Design
Academy Editions
1991
Great Britain
ISBN 1 85490 059 5

Architecture Studio
Selected and Current Works
The Images Publishing Group Pty Ltd
Australia
1996
ISBN 4-938812-62-2 C3052 P7800E

Icons of Architecture
The 20th Century
Prestel-Verlag
Germany
1998
ISBN 3-7913-1949-3

Architects’ Guide to Stainless Steel
Steel Construction Institute
Great Britain
1997
ISBN 1 85942 049 4

Structure, Space and Skin
The Work of Nicholas Grimshaw & Partners
Phaidon Press Limited
Great Britain
1993
ISBN 0 7148 2850 5

The Beaux-Arts and the Nineteenth-Century French Architecture
William Clowes (Beccles) Ltd.
Great Britain
1982
ISBN 0 500 34086 2

Patrick Berger
Opere e progettii
Œuvres et projets
Accademia di architectura dell’Università della Svizzera Italiana
Skira editore
Italy
1997, 1999
ISBN 88-8118-348-X

Domus
Settembre/September 1998 807
Archivio di Stato del Canada, Gatineau, Quebec
Canadian National Archives, Gatineau, Quebec
Editoriale Domus S.p.A.
Italy
1998

Paul Andreu
Métamorphoses du cercle
Electa France
France
1990
ISBN 2-86653-081-0

Bibliothèque Nationale de France 1989 1995
Artemis et Arc en Rêve Centre d’Architecture
France
1995
ISBN 3-7643-5590-5

GA Document Extra 10
Bernard Tschumi
A.D.A. Edita Co., Ltd.
Japan
1997
ISBN 4-87140-230-4 C1352

Arne Jacobsen
Arkitekt & Designer
Dansk Design Center / Danish Design Centre
Denmark
1996
ISBN 87-87385-45-7 (hardcover)
ISBN 87-87385-56-2 (softcover)

Arkitekten Arne Jacobsen
Arkitektens Forlag
Denmark
1957

Peter Rice
An Engineer Imagines
ellipsis london limited
Great Britain
1994
ISBN 1 89985811 3

Eco-Tech
Sustainable Architecture and High Technology
Thames & Hudson Ltd.
Great Britain
1997
ISBN 0-500-34157-5

Philippe Samyn
Architecture and Engineering 1990-2000
Birkhäuser - Publishers for Architecture
Switzerland / Austria
1999
ISBN 3-7643-6067-4
ISBN 0-8176-6067-4

Construire en acier
Publications du Moniteur
(Éditions le Moniteur)
France
1993
ISBN 2-281-19076-5

Les anges de Christians Brygge et autres
Récits d’architecture
Francis Soler par Odile Fillion
Éditions Jean-Michel Place
Institut Français d’Architecture
1995
ISBN 285 893 261 1

Das Widder Hotel in der Altstadt von Zürich
At Home In Zurich
Zeitschrift Turicum
26. Jahrgang, Nr. 4
August-September 1995
Switzerland
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Horta
Marc Vokaer, Editeur
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Teräsrakennelehti (Steel Construction Magazine). Publisher: Finnish Constructional Steelwork Association Ltd.
1/89
1/90
1/91
1/92
4/92
1/93
2/93
2/94
3/95
2/96
3/96
4/96
3/97
2/98
4/98
1/99

Drawings

6.158–6.161
Les anges de Christians Brygge et autres
Récits d’architecture
Francis Soler
par Odile Fillion
Éditions Jean-Michel Place
Institut Français d’Architecture 1995
ISBN 285-893 261-1

Other architectural drawings supplied by the architectural designers of the featured projects.

Internet sites:
http://www.edelstahl-rostfrei.de/
http://www.nickelinstitute.org/
http://www.steel-sci.org/
http://www.worldsteel.org/issf/issf_forum/
http://www.ssina.com/
http://www.assda.asn.au/

ISBN 2-87997-030-X
Diamant Building • Bd. Aug. Reyers 80 • B - 1030 Brussels • Phone +32 2 706 82-67 • Fax –69 • e-mail info@euro-inox.org • www.euro-inox.org